Abstract: Nine endophytic strains were isolated from mature fruit of red-flesh sweet pomelo（Citrus grandis） by tissue explant isolation method on 3 sorts of culture mediums，including beef extract peptone medium，PDA media and Gause's No.1 medium. By morphologic and microscopical characteristics，the 9 strains were identified as endophytic actinomycetes，and were classified into 2 genera of Norcardia（4 strains） and Streptomyces（ 5 strains）.Antimicrobial activities of these actinomycetes were determined by confronting cultivation on PDA plate method. The results showed that 6 strains performed different degrees of antagonistic activity against Escherichia coli（1 strain），Staphylococcus aureus（4 strains） and Bacillus subtilis（3 strains） ，accounting for 66.7% of all strains. And 7 strains possessed significantly higher antifungal activity against Penicillium digitatum Sacc.（7 strain），P. italicum Wehmer（3 strains） and Alternaria citri Ellis et. Pierce（3 strains） ，accounting for 77.8% of all strains，with more than 75% inhibition rate. The strains of P1 and R2 exhibited stronger antagonistic activity against the 3 kinds of citrus pathogens.