The structure of talopeptin (MK-I), a novel metallo proteinase inhibitor produced by Streptomyces mozunensis MK-23 was elucidated to be 6-deoxy-e-Ltalopyranosyloxyphospho-L-leucyl-L-tryptophan.As reported in the previous papers [1,2], a novel proteinase inhibitor talopeptin (MK-I), which shows a specific inhibitory activity against metallo proteinases, was isolated from the culture filtrate of Streptomyces mozunensis MK-23. It was also reported that talopeptin is composed of 6-deoxyaldohexose, phosphoric acid, leucine and tryptophan. In this paper, structural elucidation of talopeptin is reported.