An 1-N-((S)-.alpha.-substituted-.omega.-aminoacyl)-neamine or -ribostamycin of the formula ##STR1## wherein R is a hydrogen atom or .beta.-D-ribofuranosyl group of the formula ##STR2## and R.sub.3 is hydroxyl, amino-NH.sub.2 or acylamino group --NHR.sub.4 in which R.sub.4 is an acyl group, and n is a whole number of 1 to 4, may be produced by subjecting the corresponding O-((S)-.alpha.-substituted-.omega.-aminoacyl)-neamine or -ribostamycin of the formula ##STR3## or its hydroxyl-masked and maino-masked form, to the action of a basic medium to produce an acyl-migration product of the formula: ##STR4## and, optionally converting the amino-masking groups into hydrogen atoms and also the hydroxyl-masking group into hydroge atom in a known manner if said amino-masking groups and said hydroxyl-masking groups are present in the acyl-migration product. The 1-N-((S)-.alpha.-substituted-.omega.-aminoacyl)-neamine or -ribostamycin produced is characterized by its useful activity inhibitory to the growth of bacteria resistant to the parent substance neamine or ribostamycin.