Microorganisms isolated from wheat leaf surfaces were screened for inhibition of wheat powdery mildew. A new screening method, in which wheat leaves were inoculated with Blumeria graminis f. sp. tritici and incubated with the cultured microorganisms under non-contact conditions, was developed in our study. Among these strains, a fungus designated as Kyu-W63 had an especially strong inhibitory effect. Kyu-W63 had a strong aromatic odor when being cultured. Nuclear magnetic resonance analysis revealed that Kyu-W63 produced two types of volatile substances, 5-pentyl-2-furaldehyde and 5-(4- pentenyl)-2-furaldehyde. Although the two are known to be nematicidal substances, the antifungal activity of 5-(4-pentenyl)-2-furaldehyde is first confirmed in our study. In contrast, 5-pentyl-2-furaldehyde was found to have strong suppression activities to various fungal species in this study, although it has been reported to suppress the growth of yeast, Nematospora coryli. Strain Kyu-W63 completely agreed with Irpex lacteus in the rDNA internal transcribed spacer (ITS) sequences, and strain Kyu-W63 was inferred to be I. lacteus. Biocontrol of parsley powdery mildew, caused by Oidium sp., was examined using a filamentous fungus, Kyu-W63 that produces antifungal volatiles, for 3 years under greenhouse conditions. Kyu-W63 treatment significantly inhibited disease severity compared to control plots. In addition, Kyu-W63 suppressed other harmful fungi such as Penicillium sp. and Aspergillus sp. which are plant pathogens or human allergens existing in the environment.