Streptomyces hygroscopicus No. P247-71 (ATCC 53709) produced a novel antibiotic eponemycin which exhibited specific in vivo antitumor effect against B16 melanoma. Structural studies assigned (4S)-1, 2-epoxy-2-hydroxymethyl-4-(N-isooctanoyl-L-serylamino)-6-methylhept-6-ene-3-one to eponemycin which is unrelated to the known antitumor antibiotics.