Abstract: In order to verify the effect of temperature on the development, fecundity and biological fitness of pyridaben resistant and susceptible populations of Tetranychus truncates Ehara, the development, average life span and female egg production along with biotic fitness (calculated by using the net reproductive rate ) of two T. truncatus populations were determined at six different temperatures (16 ℃, 20 ℃, 24 ℃, 28 ℃, 32 ℃ and 36 ℃) and 16 h illumination, 60% ± 5% relative humidity. The results showed that the two T. truncatus populations completed generation development within the investigated temperature ranges and the entire developmental duration and average life-span duration shortened as temperature increased. The entire developmental duration of pyridaben resistant and susceptible populations of T. truncatus respectively were shortened by 20.0 d and 18.7 d within a temperature range of 16?36 ℃. Compared with susceptible population of T. truncatus, the resistant population had shorter developmental duration of every life stage, average life span and reproduction under low and thermophilic temperature range of 16?28 ℃. Apart from egg production (average of 17.15 eggs and 16.64 eggs for per resistant and susceptible female T. truncatus), the developmental duration, average life span and spawning period of resistant population of T. truncatus were longer than those of susceptible population of T. truncatus at a high temperature of 36 ℃. Using life parameter of net reproductive rate (R0) to determine biological fitness of the two T. truncatus populations, it was noted that biological fitness of the resistant population was less than 1 (one) in the temperature range of 16-28 ℃, while fitness of resistant population was greater than 1 (Rf =1.18, 1.19) at high temperature 32 ℃, 36 ℃. It implied that biological fitness of resistant population was significantly higher than that of susceptible population of T. truncatus at high temperature, but indifferent at low and thermophilic temperature ranges. The above results showed that the suitability of T. truncatus to high temperature increased after selection with pyridaben and the survival rate and fecundity of resistant population was obviously greater than that of susceptible population of T. truncatus at high temperature.