Three new macrolides, jaspisamides A [I], B 121, and C [31, with cytotoxic activities have been isolated from the Okinawan marine sponge Jaspis sp. and their structures determined by the spectroscopic data. This is the first isolation of macrolides from a sponge of the genus Jaspis. Several cytotoxic and antifungal macrolides containing oxazole rings have been isolated from nudibranch egg masses (14) and sponges of the genera Halicbondria (4,s) and Mycale (6). During our search for bioactive metabolites from Okinawan marine organisms (7-1 l), we examined extracts of the sponge Jaspis sp. and obtained three new cytotoxic macrolides, jaspisamides A El}, B 121, and C [3}, together with known related compounds halichondramide 14) (5), dihydrohalichondramide 151 (4), and isohalichondramide 161 (4). In this paper we describe the isolation and structural elucidation of 1-3.