A new gamma-alkylidene bicyclic butenolide designated as cochinolide (1) and its beta-glucopyranoside (3) were isolated from the root bark of Homalium cochinchinensis (Flacoutiaceae). Their structures, except absolute stereochemistries, were determined by spectroscopic means. Cochinolide (1) showed moderate antiviral activities against HSV-1 and -2.