Several members of the thiopeptide antibiotics such as thiostrepton, nosiheptide, micrococcin, sulfomycin and berninamycin induce expression of numerous genes of unknown function in Streptomyces Hvidans3). Among them, the region containing the tipA gene and its promoter region was cloned and sequenced3). TipA proved to be a regulatory protein which autogenously activates transcription of its own promoter after interacting with thiostrepton or other related thiopeptide antibiotics4). This powerful inducible promoter (ptipA) has been incorporated into a series of vectors to allow regulated expression of genes in Streptomyces. In addition, ptipA has been employed in a very sensitive and specific microbiological disc assay to screen for compounds inducing its transcription resulting in isolation of promothiocins A and B1 and geninthiocin2). In the course of our continuing screening, thioxamycin and its new derivative, thioactin were isolated from the mycelium of Streptomyces sp. DP94 (Fig. 2). The taxonomy of the producing strain, fermentation, purification and physico-chemical properties of thioxamycin were reported5) but details of its structure determination including NMR data were not presented. This paper presents isolation, fermentation, structure elucidation and tipA promoter inducing activities of thioxamycin and its new derivative, thioactin.