Pyrindamycins A (1) and B (2), two new potent antitumor antibiotics related to CC-10651~3) have been found in the culture broth of Streptomyces sp. SF2582, which was isolated from a soil sample collected at Sagamihara,Kanagawa Prefecture, Japan. The antibiotics are active against Gram-positive and Gramnegative bacteria, and exhibit strong therapeutic effects against both drug-sensitive and resistant cells of P388 leukemia in mice. In this communication, the isolation, characterization and structural elucidation of the antibiotics are reported.