The isolation and biological activities of sulfur-containing antibiotics sulfomycins I, II and III from the fermentation broth of Streptomyces viridochromogenes MCRL-0368 were reported by Egawa et ai in 1969.1} The structure of sulfomycin I was determined on the basis of chemical degradations and NMRtechniques2'3) to be a cyclic thiopeptide antibiotic represented by thiostrepton4), berninamycin3) and thiopeptin5). The structures of sulfomycins II and III, however, remained unclear. Recently, Seto and his colleagues reported aseries of new thiopeptide antibiotics, promothiocins A and B6), geninthiocin7), thiotipin8) and promoinducin9), as tip A promoter-inducing substances. In this paper, we wish to disclose the structures of sulfomycins II and III based on the ID and 2D NMRstudies.