The present invention provides compounds useful as agents for the preventionor treatment of a disease associated with abnormal plasma uric acid level andthe like.The present invention relates to fused ring derivatives represented by thefollowingformula (I) having xanthine oxidase inhibitory activities and useful as agentsfor theprevention or treatment of a disease associated with abnormality of plasmauric acidlevel, prodrugs thereof, salts thereof or the like. In the formula (I), X1 andX2represent CH or N； ring U represents aryl or heteroaryl； m represents integralnumberfrom 0 to 2； n represents integral number from 0 to 3； R1 represents a hydroxygroup,amino or C1-6 alkyl； R2 represents C1-6 alkyl, C1-6 alkoxy C1-6 alkyl or thelike.(see formula I)
