Biological studies on the predatory_, mite, Phytoseiulus persimilis A.-H. showed that the female lived longer than of the male; whereas female and male longevity averaged 14.72 and 11.5 days, respectively. The predator efficiency of consumed immature stages of Tetranychus urticae Koch, increased during the predator developmental stages as well as the adult female and male consumed 77.4 and 27.5 immatures of r urticae, respectively. At cold storage of P. persimilis eggs at 10 and 5°C for (1, 2, 3 and 4 weeks), eggs hatchability% were 100, 87.5, 70 and zero% at 10°C and 84.9, 10, 2.5 and zero% at 5°C, respectively when the stored eggs transferred at 25°C. The biological aspects of the predator P. persImills after cooling storage of its eggs at 5°C for one week, compared with the biological aspects of P. persimilis at 25°C indicated that female longevity decreased to 8.9±1.74 days comparing with 14.5±1.5 days for control. Female fecundity reduced in cooling treatment, which the number of deposited eggs per female was 19.36±6.6 eggs and it was 45.4±4.99 eggs per female in control.