A complex of novel antitumor antibiotics related to the pluramycin-group was isolated from the fermentation of actinomycete, named Streptomyces sp. HP530. The producing strain mutated frequently. The products isolated from the parent strain were designated saptomycins A, B, C1, C2 and F, while those of the mutant were named saptomycins D, E, G and H. These structures were elucidated by several NMR spectral analyses and other spectroscopic experiments.