Temperature-dependent development, longevity and mortality of the aphid parasitoid, Diaeretiella rapae (M'Intosh)(Hymenoptera: Aphidiidae) was studied at four constant temperatures, ranged between 15 C and 30 C, using the cabbage aphid Brevicoryne brassicae (L.) as host. Developmental time decreased with an increasing temperature. Mummies' developmental period was shorter at 30 C and longest at 15 C. Mummy-adult developmental period was shorter at 30 C and longest at 15 C. The shortest developmental period for egg-adult was recorded at 30 C, while the longest was at 15 C. The temperature threshold for egg-mummy, mummy-adult and egg-adult developmental periods was 2.33 C, 4.81 and 3.36 C, respectively. The Sum of Effective Temperatures was 192.3, 90.1 and 277.8 degree-days, for egg-mummy, mummy-adult and egg-adult, respectively. Mortality rate of the parasitoid was affected by temperature. The developmental rate and mortality data indicated that the optimum temperature for D. rapae was (20-25) C under laboratory conditions.