In the course of screening of a highly-productive strain of bleomycin, it was found that a mutant, which was obtained by treatment of a bleomycin-producing strain by UV-irradiation, produced a new type of bleomycin together with known bleomycins. This new type of bleomycin was named cleomycin on the basis of a structural feature that it contains a cyclopropane ring. In this communication, we report isolation, properties and structure determination of cleomycin.