A new compound 2-(4-hydroxybenzoyl) quinazolin-4(3H)-one (1) and four known compounds were isolated from a marine fungus Penicillium oxalicum 0312F1. The structure of the new compound 1 was elucidated based on the spectroscopic analysis. Bioactivity assays showed that 2-(4-hydroxybenzyl) quinazolin-4(3H)-one (2) and methyl 4-hydroxyphenylacetate (5) had potent inhibitory activity against tobacco mosaic virus (TMV), and the new compound 1 had moderate inhibitory activity against TMV and human gastric cancer cell SGC-7901.