54-Deamino-54-guanidinomonazomycin (1), a new member of the monazomycin antibiotics, and monazomycin (2) were found in the culture filtrate of the microbial strain UC8633. The producing strain was isolated from a soil sample collected in Indiana, U.S.A. and identified as a member of the genus Streptoverticillium. The antibiotics were isolated and their structures determined by NMR and MS studies. In this communication, the isolation, structure, and biological activities of 1 are reported.