The stone leek leafminer, Liriomyza chnensis (Kato), has become a serious pest on Allium spp. In several Asian countries. However, knowledge concerning the biology of L. chinensis, which affect development of control programs, is still limited. The biology of the leafminer on onion was investigated at a constant temperature of 25℃ and photoperid of 16L:8D. To distinguish different larval instars, some morphological characteristics such as the length of mouth hooks and cephalopharyngeal skelton, body and mine were measured. The length of mouth hokks and cephalopharyngeal skelton of first, second and third instars were 0.021mm and 0.089mm, 0.054mm and 0.165mm, and 0.092 mm and 0.261mm, respectively. Developmental time for the immature stages was 22.6 days; pupal development lasted slightly longer than the combined egg and larval stages. The females laid a mean of 108 eggs and fed on 1013.9 punctures during an average lifespan of 9 days, Feeding and fecundity peaked at age 5 days. The intrinsic rate of natural increase (rm)(day[-1]), net reproduction (Ro), and generation time(T)(day) were 0.099, 14.3 and 27.1, respectively.