As new compounds are now synthetized 5-deoxy-5,5-difluoro derivatives of aminoglycosidic antibiotics of neamine, kanamycin A-series, kanamycin B-series, gentamicin-series and seldomycin-series. Further, the 1-N-(.alpha.-hydroxy-.omega.-aminoalkanoyl) derivatives are synthetized from 5-deoxy-5,5-difluorokanamycins A and B, as well as their analogues now obtained. The 5-deoxy-5,5-difluoro derivatives of the aminoglycosidic antibiotics now provided according to this invention have such antibacterial activities enhanced much more than or equal to those of the respectively corresponding parent aminoglycosidic antibiotics, while these 5-deoxy-5,5-difluoro derivatives exhibit values of the 50% lethal dosage (LD.sub.50) which are improved remarkably better when they are intravenously administered to mice, so that they have remarkedly reduced toxicities to mammals.