Penicillide, having a 5H, 7H-dibenzo［b,g］［1,5］ dioxocin-5-one skeleton, was isolated from the culture broth of Penicillium sp. F60760 as a nonpeptide inhibitor of calpain, a calcium-activated papain-like protease. The $IC_50$ value for the effect of penicillide against m-calpaln was $7.1{mu}M$. However, penicillide did not inhibit papain at a concentration of $200{mu}M$. These results suggest that penicillide is a new class of nonpeptide calpain inhibitor having an eight membered lactone ring.