An Jung-sik's original given name was Uksang (昱相); his sobriquets were Simjŏn (心田) and Pubuwong (不不翁), the latter used in his final years. He was accomplished in every category of painting and was equally skilled in clerical and running-script calligraphy. Together with Cho Sŏk-jin (趙錫晉), he formed the twin pillars of the late Chosŏn painting world and served as the bridge between the art of the dynastic twilight and the emerging world of modern painting. He and Cho Sŏk-jin both studied under Owŏn Chang Sŭng-ŏp (張承業) from an early stage in their careers and were profoundly influenced by him. In 1902 he participated in the Directorate for the Painting of the Royal Portrait. The most consequential episode of his career, however, was his service as the founding president of the Calligraphy and Painting Association (書畵協會), organized in 1918 in response to the duplicitous cultural policies of the Japanese colonial administration, through which he worked to sustain and promote the nation's indigenous traditions of painting and calligraphy. As a consequence, he was imprisoned in the aftermath of the March First Independence Movement and died at the age of fifty-nine from the effects of his incarceration.
He worked most extensively in landscape, but left behind a substantial body of work in bird-and-animal painting and figure painting as well. This six-panel folding screen of immortals — comprising Liu Hai Playing with a Toad (劉海戱蟾), Zhang Guo-lao (張果老), Red Pine Master (赤松子), and Anqi Sheng (安期生) — both exemplifies the characteristic qualities of his figure painting manner and reflects throughout the strong imprint of Chang Sŭng-ŏp's style. The figures' long, narrow eyes, prominent cheekbones, and the appearance of the long-bearded elders are closely akin to the figures in Chang Sŭng-ŏp's Immortal Gathering Mushrooms of Immortality (仙人採芝圖) discussed earlier. The complex, sharply angular drapery folds, the twisted forms of the pine trunks, and the burr-like rendering of pine foliage are equally characteristic of Chang Sŭng-ŏp's manner. In the schematically rendered clouds and mountain texture strokes, however, the progressive mannerization of the Chang Sŭng-ŏp style is also in evidence. The Liu Hai subject appears in a work of nearly identical iconography in the collection of Seoul National University Museum, and An Jung-sik's colleague Cho Sŏk-jin left a closely similar painting differing only in the orientation of the figure. Liu Hai Playing with a Toad was a subject treated by numerous painters from the late Chosŏn period onward, among them Sim Sa-jŏng (沈師正) and Paek Ŭn-bae (白殷培). The subject of Zhang Guo-lao riding his donkey in reverse was likewise depicted by many painters, with Kim Hong-do's masterpiece of the subject preserved in the Gansong Art Museum standing as the most celebrated example.