The functional response of Neoseiulus californicus (McGregor), a phytoseiid predator, was studied on different life stages of twospotted spider mite, Tetranychus urticae Koch, on leaves of apple, Malus domestica Borkh, during a period of 24 hours at 27 ± 2°C and 60% relative humidity. According to Holling's (1959) model, the functional response was Type II. The rate of instantaneous discovery (a') values were 0.9352 for eggs, 0.9260 for larvae, 0.8320 for nymphs, and 0.6786 for female adults, while handling time (Th) values were 0.0122, 0.0116, 0.0126, and 0.0532 for the same stages, respectively.