Three new macrolides, jaspisamides A [1], B [2], and C [3], 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 (1-4) and sponges of the genera Halichondria (4,5) and Mycale (6). During our search for bioactive metabolites from Okinawan marine organisms (7-11), we examined extracts of the sponge Jaspis sp. and obtained three new cytotoxic macrolides, jaspisamides A [1], B [2], and C [3], together with known related compounds halichondramide [4] (5), dihydrohalichondramide [5] (4), and isohalichondramide [6] (4). In this paper we describe the isolation and structural elucidation of 1-3.