There is provided a heteroaryl 5-thio-.beta.-D-glucopyranoside compound of the following formula, which has an inhibitory effect on SGLT2 activity, or a pharmaceutically acceptable salt thereof or a hydrate thereof. There is also provided a pharmaceutical preparation, particularly a prophylactic or therapeutic agent for diabetes, diabetes-related diseases or diabetic complications, which comprises such a compound as an active ingredient. ##STR00001##