Three cytotoxic cytochalasins were isolated and characterized from Xylaria sp.rn(LEP-12) cultured on a sterile moist rice. The fungus grown on the above medium for 14rndays at room temperature produced three cytochalasins, identified by spectroscopic methodsrnand chemical derivatizations as cytochalasin Q (3), 19,20-epoxycytochalasin Q (4) andrn19,20-epoxydeacetylcytochalasin Q (5). However only compounds 3 and 4 could bernisolated when the fungus was allowed to grow in the medium for 18 days. This is the firstrnreport of cytochalasin Q from the genus Xylaria. All three cytochalasins were lethal tornbrine shrimp with LCJO value of 5, 5 and 2 /xg/ml for compounds 3, 4 and 5, respectively