A new 1-N-(.omega.-aminoalkanesulfonyl) derivative of an aminoglycosidic antibiotic such as ribostamycin, 3'-deoxy- or 3',4'-dideoxy-ribostamycin, kanamycin A or B, and 3'-deoxy- or 3',4'-dideoxy-kanamycin B exhibits a broader, antibacterial spectrum than the parent aminoglycosidic antibiotic and is useful in the therapeutic treatment of infections caused by gram-positive and gram-negative bacteria including drug-resistant strains thereof. The aforesaid derivative may be made by reaction between the parent antibiotic and an amino-protected .omega.-aminoalkanesulfonic acid halide and removal of the amino-protecting group from the condensation product.