Abstract: The toxicities,protective and curative activities,and persistence effects of azoxystrobin and pyraclostrobin against Erysiphe cichoracearum causing tobacco powdery mildew were studied through tobacco seedling assays.The results presented that azoxystrobin and pyraclostrobin both strongly inhibited the disease development,with EC50 values of 7.62 and 9.90 μg/mL,respectively;and they showed protective and curative effects against E.cichoracearum with EC50 values of 8.76,12.34 μg/mL, and 17.32,23.40 μg/mL,respectively.The two compounds had long persistence against E.cichoracearum on tobacco seedlings,with control efficacy of 94.45% and 88.53% respectively,when inoculation 30 days after treatment with 56.25 g(a.i.)/hm2 for two sprays.Azoxystrobin and pyraclostrobin both could protect the newly growing leaves against E.cichoracearum, and they were safe to tobacco seedlings at the concentration tested in this study.