Thiazohalostatin is a new cytoprotective substance produced by Actinomadura sp. HQ24. In the screening for new cytoprotective substances, Actinomadura sp. HQ24 was found to produce novel substances named thiazohalostatin. In the preceding paper1}, we described the fermentation, isolation and biological properties of thiazohalostatin. This paper describes the physico-chemical properties and structural studies of thiazohalostatin. Its structure was elucidated as shown in Fig. 1 by NMR spectral analyses and chemical modifications. Thiazohalostatin was found to possess a novel skeleton containing trichloropyrrole and thiazoline ring moieties.