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. 5 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 Ce-io aryl or the like R" independently 10 represents a hydrogen atom, a hydroxy group, Ci-e 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 independently represents a hydrogen atom, a halogen atom, Ci-e alkyl or the like.
