308 isolates of Ampelomyces sp. were isolated from powdery mildew fungi of 73 plant species in Korea for selection of biocontrol agents. An isolate 94013 isolated from powdery mildew fungus of red bean was selected as an effective biological control agent against cucumber powdery mildew in greenhouse. The morphological characteristics of the isolate is as follows. Pycnidia were sub-globose or elongated to pyriform, pale to dark brown, 52.5~82.5 × 35.0~47.5 (ave. 62.5 × 40.5)µm, and conidia were guttulate, straight cylindrical to fusiform, pale brown, 5.0~8.0 × 2.5~4.3 (ave. 6.0×3.0)µm. The isolate 94013 was identified as Ampelomyces quisqualis by morphological characteristics and rDNA ITS sequencing. The isolate A. quisqualis 94013 was different from that of the commercial product AQ10 R in the rDNA ITS sequence.