Temperature is the main abiotic factor influencing the performance of natural enemies. The effect of temperature on the developmental rate of Phytoseius plumifer (Canestrini & Fanzago), feeding on Tetranychus urticae Koch, was determined at seven constant temperatures of 15, 20, 25, 27, 30, 35 and 37°C. Eggs did not hatch at 10°C and 40°C. Total developmental time from egg to adult emergence at the mentioned temperatures was estimated to be 27.6, 15.9, 8.00, 6.8, 6.6, 5.3 and 7.5 days, respectively. Developmental time decreased with increasing temperature from 15 to 35°C. The estimated lower temperature threshold for the entire developmental time and the effective accumulative temperature (thermal constant) of P. plumifer using the Ikemoto & Takai linear model were 10.72°C and 125.3 degree-days (DD), and using the common linear model were 10.46°C and 125.3 DD, respectively. Data were fitted to various nonlinear developmental rate models and the thermal thresholds (T_min and T_max) and optimal temperature (T_opt) for developmental rate were determined. Data were fitted to eight models appropriately, however, the Ikemoto and Takai linear model and Briere 2 models were recommended for the description of temperature-dependent development of P. plumifer. Temperature-dependent development data, thermal requirements and temperature thresholds can be used to predict the occurrence, number of generations and population dynamics of P. plumifer as an important biocontrol agent of T. urticae.