An insecticidal compound was isolated from Penicillium sp. TAMA 71 and showed 82% mortality against green peach aphid (Myzus persicae) at 100 ppm. The chemical structure of the compound was determined by X-ray crystallographic analysis to be identified as oxalicine B, and its NMR data were compatible with the chemical structure. A part of the known 1 H NMR assignment was incorrect and was corrected. Insecticidal, miticidal and fungicidal tests were conducted at 500 ppm using three different insects, a mite and two plant pathogenic fungi besides the aphid to show 32% mortality and weak antifeeding activity against only western flower thrips (Frankliniella occidentalis) larvae.