The development, survival, and reproduction of Euseius nicholsi (Ehara & Lee) (Acari: Phytoselidae), an important and rapacious predatory mite that feeds on Tetranychus cinnabarinus (Boisduval), were evaluated at six constant temperatures between 19°C and 32°C. The temperature range 22°C to 28°C was found to be optimal for development and reproduction of the mites. Both were significantly impaired at temperatures higher than 28°C. At 30°C and 32°C, survival rates were significantly reduced. At all temperatures, the egg incubation period was the longest developmental stage, accounting for 40% to 45% of total development time. The sex ratios (female:male) of the offspring at the six temperatures (19, 22, 25, 28, 30 and 32°C) were 1.46:1, 1.35:1, 1.32:1, 1.52:1, 1.65:1 and 1.71:1, respectively. The lowest sex ratio occurred at 25°C, suggesting that this was the natural temperature for this species. At 25°C and 28°C, the population doubling times of E. nicholsi were 4.27 d and 3.13 d, respectively, indicating that these were appropriate temperatures for population growth. We conclude that the optimal temperature range for the development of E. nicholsi was 22°C to 28°C and that the most suitable temperature for both development and reproduction of the mites was 25°C.