Interactions betweenSporormiellasimilisKhan & Cain and the blue-stain fungusOphiostomapiliferum(Fr.) H. & P. Sydow, both isolated fromPopulustremuloidesMichx. wood, were investigated.Sporormiellasimilissignificantly reduced the growth ofO.piliferumin vitro when grown in dual culture, in addition to inhibiting the growth ofO.piliferumon agar media and in liquid culture when treated with a culture filtrate ofS.similis.Ophiostomapiliferumfailed to colonizeP.tremuloideswood chips when they were preinoculated withS.similis. Ten known compounds were isolated and identified from the culture filtrate ofS.similis. These compounds showed varied fungitoxic effect againstO.piliferumat concentrations of 1 to 1000 μg/mL. The potential forS.similisas a biological control agent againstO.piliferumonP.tremuloidesis discussed.