Like many other Chinese historical figures, Chiang used several names throughout his life. The name inscribed in the genealogical records of his family is Chiang Chou-t‘ai (Chinese: 蔣周泰; pinyin: Jiǎng Zhōutài; Wade–Giles: Chiang Chou -t‘ai ). This so-called "register name" (譜名) is the one by which his extended relatives knew him, and the one he used in formal occasions, such as when he was married. In deference to tradition, family members did not use the register name in conversation with people outside of the family. The concept of a "real" or original name is/was not as clear-cut in China as it is in the Western world. In honor of tradition, Chinese families waited a number of years before officially naming their children. In the meantime, they used a "milk name" (乳名), given to the infant shortly after his birth and known only to the close family. So the name that Chiang received at birth was Chiang Jui-yüan (Chinese: 蔣瑞元; pinyin: Jiǎng Ruìyuán).

In 1903, the 16-year-old Chiang went to Ningbo as a student, and chose a "school name" (學名). This was the formal name of a person, used by older people to address him, and the one he would use the most in the first decades of his life (as a person grew older, younger generations would use one of the courtesy names instead). Colloquially, the school name is called "big name" (大名), whereas the "milk name" is known as the "small name" (小名). The school name that Chiang chose for himself was Chih-ch‘ing (Chinese: 志清; pinyin: Zhīqīng; Wade–Giles: Chih-ch‘ing, which means "purity of aspirations"). For the next fifteen years or so, Chiang was known as Chiang Chih-ch‘ing Chinese: 蔣志清; pinyin: Jiang Zhīqīng; Wade–Giles: Chiang Chih -ch‘ing . This is the name by which Sun Yat-sen knew him when Chiang joined the republicans in Kwangtung in the 1910s.

In 1912, when Chiang was in Japan, he started to use the name Chiang Kai-shek (Chinese: 蔣介石; pinyin: Jiǎng Jièshí; Wade–Giles: Chiang Chieh -shih ) as a pen name for the articles that he published in a Chinese magazine he founded: Voice of the Army (軍聲). Jieshi is the pinyin romanization of this name, based on Standard Chinese, but the most recognized romanized rendering is Kai-shek which is in Cantonese romanization. Because the Republic of China was based in Canton (a Cantonese-speaking area), Chiang (who never spoke Cantonese but was a native Wu speaker) became known by Westerners under the Cantonese romanisation of his courtesy name, while the family name as known in English seems to be the Mandarin pronunciation of his Chinese family name, transliterated in Wade–Giles.

"Kai-shek" soon became Chiang's courtesy name (字). Some think the name was chosen from the classic Chinese book the I Ching; "介于石"; '[he who is] firm as a rock', is the beginning of line 2 of Hexagram 16, "豫". Others note that the first character of his courtesy name is also the first character of the courtesy name of his brother and other male relatives on the same generational line, while the second character of his courtesy name shih (石—meaning "stone") suggests the second character of his "register name" tai (泰—the famous Mount Tai). Courtesy names in China often bore a connection with the personal name of the person. As the courtesy name is the name used by people of the same generation to address the person, Chiang soon became known under this new name.

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Chiang was born on 31 October 1887, in Hsikow, a town in Fenghua, Zhejiang, China, about 30 kilometers (19 mi) west of central Ningbo. He was born into a family of Wu Chinese-speaking people with their ancestral home—a concept important in Chinese society—in Heqiao, a town in Yixing, Jiangsu, about 38 km (24 mi) southwest of central Wuxi and 10 km (6.2 mi) from the shores of Lake Tai. He was the third child and second son of his father Chiang Chao-Tsung [zh] (also Chiang Su-an; 1842–1895; 蔣肇聰) and the first child of his father's third wife Wang Tsai-yu [zh] (1863–1921; 王采玉) who were members of a prosperous family of salt merchants. Chiang's father died when he was eight, and he wrote of his mother as the "embodiment of Confucian virtues". The young Chiang was inspired throughout his youth by the realization that the reputation of an honored family rested upon his shoulders. He was a naughty child. At a young age he was interested in the military. As he grew older, Chiang became more aware of the issues that surrounded him and in his speech to the Kuomintang in 1945 said:

As you all know I was an orphan boy in a poor family. Deprived of any protection after the death of her husband, my mother was exposed to the most ruthless exploitation by neighbouring ruffians and the local gentry. The efforts she made in fighting against the intrigues of these family intruders certainly endowed her child, brought up in such an environment, with an indomitable spirit to fight for justice. I felt throughout my childhood that my mother and I were fighting a helpless lone war. We were alone in a desert, with no available or possible assistance could we look forward to. But our determination was never shaken, nor was hope abandoned.

In early 1906, Chiang cut off his queue, the required hairstyle of men during the Ch‘ing dynasty, and had it sent home from school, shocking the people in his hometown.

Chiang grew up at a time in which military defeats, natural disasters, famines, revolts, unequal treaties and civil wars had left the Manchu-dominated Ch‘ing dynasty unstable and in debt. Successive demands of the Western powers and Japan since the Opium War had left China owing millions of taels of silver. During his first visit to Japan to pursue a military career from April 1906 to later that year, he describes himself as having strong nationalistic feelings with a desire, among other things, to 'expel the Manchu Ch‘ing and to restore China'. In a 1969 speech, Chiang related a story about his boat trip to Japan at nineteen years old. Another passenger on the ship, a Chinese fellow student who was in the habit of spitting on the floor, was chided by a Chinese sailor who said that Japanese people did not spit on the floor, but instead would spit into a handkerchief. Chiang used the story as an example of how the common man in 1969 Taiwan had not developed the spirit of public sanitation that Japan had. Chiang decided to pursue a military career. He began his military training at the Baoding Military Academy in 1906, the same year Japan left its bimetallic currency standard, devaluing the Japanese yen. He left for Tokyo Shinbu Gakko, a preparatory school for the Imperial Japanese Army Academy intended for Chinese students, in 1907. There, he came under the influence of compatriots to support the revolutionary movement to overthrow the Manchu-dominated Qing dynasty and to set up a Han-dominated Chinese republic. He befriended Chen Qimei, and in 1908 Chen brought Chiang into the Tungmenghui, an important revolutionary brotherhood of the era. Finishing his military schooling at Tokyo Shinbu Gakko, Chiang served in the Imperial Japanese Army from 1909 to 1911.