The developmental time of larvae of mealworm beetle, Tenebrio molitor was studied at six temperatures ranging from 17 to 30℃ with 60~70% RH, and a photoperiod of 14L:10D. Mortality of 1st~13th larva was very low at 17 and 20℃ but did not die over 22℃. Developmental time of larva decreased with increasing temperature. The total developmental time was longest at 17℃ (244.3 days) and shortest at 30℃ (110.8 days), suggesting that the higher temperature, the faster development period. The lower developmental threshold temperature and effective accumulative temperatures for the total larval stages were 6.0℃ and 2564.1 day-degrees. The relationship between developmental rate and temperature fitted a linear model and nonlinear model by Logan-6 (r2=0.95). The distribution of completion of each development stage was well described by the 3-parameter Weibull function (r2=0.89).