A pharmaceutical composition comprising a combination of(A) a 1-thio-D-glucitol compound represented by the general formula (I)and(B) at least one member of the group consisting of biguanides, insulin secretagogues, insulin sensitizers, insulins, dipeptidyl peptidase IV inhibitors, α-glucosidase inhibitors, and GLP-1 mimetics, has superior efficacy in preventing or treating diabetes mellitus, diseases associated with diabetes mellitus, or complications of diabetes mellitus and yet it causes no appreciable side effects.
