Three unusual alkyhydrazide natural products, named hydrazidomycin A (1), B (2) and C (3), were isolated from the chloroform extract of a Streptomycesatratus culture, and their structures were elucidated by MS and NMR techniques. Hydrazidomycins A-C exhibited moderate to strong cytotoxic activities in a panel of 42 cell lines, with hydrazidomycin A being the most potent compound (mean IC(50)=0.37 μM).