6-(p-Hydroxyphenyl)-2H-3,4-dihydro-1,1-dioxo-1,4-thiazine (1) has been isolated from the marine sponge Anchinoe tenacior, along with a novel tripeptide with a C-terminal trans-4-hydroxystirylamino residue (2). In our continuing search for bioactive compounds from marine organisms, we reported previously the isolation of a dimeric peptide alkaloid, anchinopeptolide A, from the Mediterranean sponge Anchinoe tenacior.1 Here we describe the isolation and structure elucidation of an unique metabolite 1, which incorporates a 1,1-dioxo-1,4-thiazine ring, and of a new tripeptide (2), from the sponge A. tenacior.