Bioassay-directed fractionation of the lipophilic extract of a marine sponge Sarcotragus sp. led to the isolation of a known trisoxazole containing macrolide, mycalolide B (1). Its structure was identified by NMR and MS analyses. This is the first report on the isolation of macrolide from a sponge of the genus Sarcotragus (Order: Dictyoceratida).