A strain of Pythium oligandrum isolated from soybean, grown in a commercial field in Osaka, Japan, was characterized by species identification and suppression of soybean damping off caused by P. aphanidermatum and P. myriotylum. The morphology and hyphal growth temperature of the P. oligandrum strain corresponded with those of the original description of P. oligandrum. rDNA-ITS sequences of the P. oligandrum strain were highly matched to those of the type strain of the species. The P. oligandrum strain was mycoparasitic toward P. aphanidermatum and P. myriotylum, and significantly suppressed soybean damping off caused by them. This is the first report of the effectiveness of P. oligandrum on soybean damping off pathogens.