A complex of the antitumor antibiotic BBM-928 was produced by an actinomycete strain No. G455-101. Four components, BBM-928 A, B, C and D, were isolated in crystalline form and characterized. They were shown to be cyclic depsipeptide antibiotics containing a quinoline nucleus as the chromophore. BBM-928 A is a monoacetyl derivative of BBM-928 B and a diacetyl derivative of BBM-928 C. BBM-928 components exhibit antimicrobial activity against Gram-positive and acid-fast bacteria. BBM-928 A is highly active in mice against various experimental tumors including leukemia P388, leukemia L1210, melanoma B16, LEWIS lung carcinoma and sarcoma 180. BBM-928 B is less active than BBM-928 A, and BBM-928 C has no antitumor activity.