Antimicrobial activities of baumycins described were tested by the broth dilution method and the results are shown. Baumycins A1, A2, C1 and C2 showed a strong inhibition against Gram-positive bacteria, while baumycins B1 and B2 showed only weak activity. Baumycins A1 and A2 showed a strong inhibition against the growth and syntheses of RNA and DNA of cultured L1210 mouse leukemia cells: RNA synthesis inhibition (%) at 0.5 .mu.g/ml, A1, 64.7; A2, 60.6; B1, 17.6; B2, 14.3: DNA synthesis inhibition (%) at 1 .mu.g/ml, A1, 69.6; A2, 40.4; B1, 25.0; B2, 6.7.