Abstract: Twenty etridiazole-resistant mutants of Phytophthora drechsleri were obtained by ultraviolet irradiation,and some of their biological characteristics were studied in vitro. The results showed that frequency of mutation in P.drechsleri that resistant to etridiazole was higher than that resistant to metalaxyl,while etridiazole-resistant level was much lower than that of metalaxyl-resistance,the resistance factor(RF) for etridiazole was ranged from 1.32 to 4.31.The resistance to etridiazole was stable in the process of continuous transfer cultivation and long conservation under room temperature.As compared to their parental sensitive isolate,the growth rates of mutants changed more or less.In addition,there was no cross-resistance between etridiazole and metalaxyl or dimethomorph.