Abstarct: Predatory mite Amblyseius swirskii is a suitable predator which feeds on Tetranychus urticae and Bemisia tabaci. With regard to the role of the predator and to understand more aspects of their lives, in this research life table and prey preference on immature stages of T. urticae and B. tabaci were studied. The life table parameters of A. swirskii under laboratory conditions with 25±2 °C, 70±5% relative humidity and the photoperiod of 16L: 8D hours, with 100 replicates at the same time on two different preys, T. urticae and B. tabaci were studied. Predator eggs were settled on cucumber leaf, individually. The date of entering of each larval as well as adult stage into the next stage was recorded. When the adults emerged, females and males were paired kept together in rearing Petri dishes and every day, all eggs were counted and recorded. The data of life table were determined by age-stage two-sex life table model. Duration of different instar stages of A. swirskii when fed on T. urticae and B. tabaci showed no significant difference (egg, P = 0/41, t = -0/81, protonymph, P = 0/097, t = -1/67, Deutonymph, P = 0/11, t = 1/58, adult, P = 0/50, t = 0/67), except larva (P = 0/0007, t = -3/50) and Preadult period showed significant difference (P = 0/002, t = -3/15). Also a comparison of life table parameters, showed no significant difference in mean generation time (T) of A. swirskii on T. urticae and B. tabaci. The intrinsic rate of increase (r), the net reproductive rate (R0) and the finite rate of increase (λ) of A. swirskii on T. urticae have significant difference with predatory mite A. swirskii fed on B. tabaci. For the predator preference experiment on immatures of T. urticae and B. tabaci (eggs, nymphs 1 and 2 ( with densities (12: 12, 6: 6 and 3: 3) were used. Also for prey stage preference of predator was determined using immature stages of T. urticae and B. tabaci in three treatments for each prey species. These treatments consisted T. urticae (eggs- first instar nymphs, eggs- second instar nymphs and first instar nymphs- second instar nymphs( with densities 20: 20, 20: 20 and 20: 20 and for B. tabaci were with densities 8: 8, 8: 8 and 8: 8, respectively. Same aged females of A. swirskii starvation for 24 hours were added to the leaf discs singly. All experiments were done on cucumber leaf discs at similar conditions as above (the same as life table experiments condition). After 24 hours, the number of individuals consumed was recorded. Amblyseius swirskii females consumed significantly eggs and second instar nymphs of T. urticae than B. tabaci (df = 24, P ˂ 0/0001, t = 10/80 and df = 24, P = 0/63, t = 0/48, respectively) and there was no statistical difference between first instar nymphs of two prey species (df = 24, P = 0.63, t = 0/48). Also the results of prey stage preference showed that there was a significant difference between eggs- first instar nymphs, eggs- second instar nymphs and first instar nymphs- second instar nymphs of T. urticae and B. tabaci (t = 46.16, df = 38, P < 0.0001 and t = 8.73, df = 38, P < 0.0001; t = -46.95, df = 38, P < 0.0001 and t = -63.84, df = 38, P < 0.0001; t = -67.85, df = 38, P < 0.0001 and t = -98.67, df = 38, P < 0.0001). The findings of this research, as basic information could be used in biological control.