Tallysomycin S10b is a biosynthetic derivative of tallysomycin B obtained by precursor amine-feeding fermentation. Tallysomycin S10b contains 1,4-diaminobutane as the terminal amine moiety in place of spermidine of tallysomycin B, and its assigned structure was verified by carbon-13 NMR spectrum. The antitumor activity of tallysomycin S10b was comparable to that of tallysomycin A against sarcoma 180 but less active than the latter against leukemia P388. Tallysomycin S10b was less toxic than tallysomycin A in terms of acute and subacute LD50 values. The nephrotoxic potential of tallysomycin S10b in rats was less than that of tallysomycin A.