Abstract: This study aimed to evaluate the efficiency of Bacillus pumilus AR03 against Altenaria alternata and Erysiphe cichoracearum. The antagonistic activities were studied in the way of coculture on plate, inhibition of pathogen conidia germination on concave slides and LB agar medium. In the investigation, the water suspension of living cells of strain AR03, at 3×10⁸ cfu·mL^-1 had a remarkable inhibition effect on hyphae growth and conidia germination of A. alternata and caused hyphae deformation, shorter and swollen nodes, winding hyphae accumulation, abnormal tubes with tips expanded or deformed. Conidia did not germinate and the tissues of compartment became swollen or formed a round spherical bubble. In addition, the inhibition rate of conidia germination of E. cichoracearum was 91.3% and 69.3%, respectively when treated with strain AR03 at 1×10⁷cfu·mL^-1 and 1.5×10⁶ cfu·mL^-1. Conidia treated by living cells of AR03 became swollen, deformed, the protoplasm of conidia shrinked, disintegrated gradually and separated from the conidia wall. And some conidia were hollow because the protoplasm leaked out from inside. Greenhouse results revealed that the effects of living cells of AR03 with different concentrations were significantly different. Bacterial suspension of AR03 at 3×108 cfu·mL^-1 was strongly antagonistic to E. cichoracearum with the control efficiencies 7 days and 15 days after treatment of two spays being 83.8% and 90.3%, respectively, while the control efficiencies of AR03 at 3×106 cfu·mL^-1 were 70.0% and 73.3%, respectively. Strain AR03 had a long persistence against powdery mildew more than 30 days.