The structures of deltamycins A1,A2,A3 and A4 belonging to the basic macrolide family of antibiotics were determined mainly from their spectral properties. Deltamycin A4 was identified as carbomycin A having an isovaleryl group on the mycarose moiety of the molecule. Deltamycin A1,A2 and A3 possess similarities to the structure of deltamycin A4, but they have acetyl, propionyl and n-butyryl group, respectively, in the place of isovaleryl group of deltamycin A4. These structures were confirmed by chemical synthesis from deltamycin X (4''-O-deacyldeltamycin) and the corresponding acyl chlorides.