Since 2014, some Welsh onion and carrot fields have been damaged by Bradysia sp., dark-winged fungus gnat（Diptera: Sciaridae）, in the northern region of Saitama Prefecture, Japan. Bradysia impatiens（Johannsen）are also known as important insect pests in various crops. In the present study, we examined the effects of temperature on the development and reproduction of Bradysia sp. and B. impatiens reared on rice bran at constant temperatures of 11, 16, 20, 25, and 30°C. The developmental periods from egg to adult emergence of Bradysia sp. were longer than those of B. impatiens at all temperatures. In Bradysia sp., 112.8 days and 26.6 days were required for development of adult females at 11°C and 25°C, respectively, in comparison with 93.3 days and 21.4 days for B. impatiens. The intrinsic rates of natural increase at 11, 16, 20, 25, and 30°C of Bradysia sp. were −0.006, 0.023, 0.043, 0.100, and −0.030 and those of B. impatiens were 0.004, 0.058, 0.103, 0.111, and 0.062, respectively. The tolerance of Bradysia sp. to low temperatures and high temperatures is lower than B. impatiens.