In the course of screening for new microbial bioactive metabolites, the culture broth of Streptomyces sp. MK251-43F3 showed inhibitory activity in the dipeptidyl peptidase IV (EC 3.4.14.5, DPP-IV, CD26) assays1}. DPP-IV, one of exopeptidases, is featured by the preferential cleavage of X-L-Pro and X-L-Ala from the NH2 terminus of oligopeptides2) and cleaves several biologically important peptides including chemokines3~5) and peptide hormones6'7). Therefore, DPP-IV inhibitors are currently tested as therapeutic agents for immune-related disorders8'9) and type 2 diabetes10'11}. We isolated sulphostin (1) from the culture broth of Streptomyces sp. MK251-43F3 together with its epimer (2), which was found to be formed during the isolation process (Fig. 1). In this paper, we briefly report on the production, isolation and structure elucidation of 1 and 2.