Abstract: To select the drug-resistant strain, the Streptomyces purpeofuscus YSSPG3 was treated by chemical mutagen(Ethyl methane sulfonate,Sodium azide and 5-bromouracil)with different concentration,and then these mutation strains were screened out through the carbendazim and chlorothalonil.The drug resistant concentrations of four mutant strains tolerant to carbendazim were 3 500 mg/L,with EC₅₀ value ranging from 3 202.58 to 3 722.20 mg/L, while the drug-resistance of mutation strains induced by Sodium azide in the concentration of 8 mmol/L were the strongest with EC₅₀ value of 3 722.20 mg/L. It was also found that the resistance of resistant strains to carbendazim was stably inherited after continuous subculturing for 10 times. Meanwhile, the resistance tochlorothalonil of five mutation strains of Streptomyces purpeofuscus YSSPG3 could grow well when chlorothalonil concentration was 1 500 mg/L and the EC₅₀ value of these strains tested to chlorothalonil ranged from 1 301.97-1 960.20 mg/L. These results of drug-resistance experiment showed that the mutant strains which were treated by Sodium azide(8 mmol/L)presented the best resistance to chlorothalonil, with the EC₅₀ value reaching 1 960.20 mg/L.Under successive transfer culture, their drug-resistance heredity was also very stable.