Abstract: Tetranychus urticae is one of the most economically important agricultural pests,which infests over 30 species of greenhouse and field crops. Because of a serious developmentof acaricide resistance in T. urticae populations, it has become more and more intractable tomanage this pest in many areas worldwide. Physical and biological control using UVB radiationand phytoseiid mite Neoseiulus californicus respectively are developing, especially instrawberry greenhouse in Japan. Plants are irradiated with UVB at midnight for avoidingphotoreactivation of spider mites. We simulated the irradiation condition in strawberrygreenhouse in a laboratory and evaluated the effects of temperature on egg hatchability of T.urticae and N. californicus. We reported that for both T. urticae and N. californicus, at the sameUVB radiation intensity, more eggs hatched in high temperature than low temperature.Moreover, T. urticae eggs were more sensitive than N. californicus eggs under the sameradiation intensity. It proves that low temperature can strengthen the control effect of UVBradiation against T. urticae. Higher hatchability of N. californicus eggs is advantageous tocombine the phytoseiid mites with UVB method in the practical application for the greenhouse.