The present invention provides compounds useful as agents for the prevention or treatment of a disease associated with abnormal serum uric acid level and the like. The present invention relates to fused heterocyclic derivatives represented by the following formula (I) having xanthine oxidase inhibitory activities and useful as agents for the prevention or treatment of a disease associated with abnormality of serum uric acid level, or prodrugs thereof, or pharmaceutically acceptable salts thereof. In the formula (I), ring U represents C 6-10 aryl or the like； R 1 independently represents a hydrogen atom, a hydroxy group, C 1-6 alkyl or the like； m represents an integral number from 1 to 2； ring Q represents 5-membered heteroaryl； n represents an integral number from 1 to 3； R 2 independently represents a hydrogen atom, a halogen atom, C 1-6 alkyl or the like.
