The pathogenic effects of Purpureocillium lilacinum (Thom) (Luangsaard, Houbraken, Hywel-Jones & Samson) and Isaria farinosa (Holmsk.) (Sordariomycetes: Hypocreales) Fries on the two spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae) were investigated under laboratory conditions. The effects of the fungi on Neoseiulus californicus (McGregor) (Acari: Phytoseiidae), an important predatory mite of T. urticae, were also determined. It was found that the entomopathogenic fungi can cause high mortality rates in both phytophagous and predatory mites. While entomopathogens caused 90% and more mortality in T urticae under 85% and 95% r.h. the mortality percentages caused by P. lilacinum and I. farinosa decreased to 84.72% and 68.71% respectively. I. farinosa caused 100% mortality in N. californicus on day 4 after inoculation. The mortality rate of the predatory mite inoculated with P lilacinum could reach 88% on day 4 after inoculation. It was found that I. farinosa showed a higher mortality on the predatory mite than P lilacinum.