Cyclothiazomycin is a novel renin inhibitor produced by Streptomyces sp. NR 0.516 (IC50 1.66 μM). Its molecular formula was determined to be C59H64N18O14S7 (MW 1472) based on high-resolution FAB mass and NMR spectroscopy. Five fragments of cyclothiazomycin containing thiazole, thiazoline, and heterocyclic chromophore were clarified by extensive 2D-NMR experiments.