The present invention provides an 8-modified purinenucleoside derivative which is useful for diseases associated with an abnormality of plasma uric acid level. An 8-modified purinenucleoside derivative represented by the following formula (I), a prodrug thereof or a pharmaceutically acceptable salt thereof, or a hydrate or solvate thereof, is useful for the prevention or treatment of gout, hyperuricemia, urinary lithiasis, hyperuricemic nephropathy or the like. In the formula, n is 1 or 2; R.sup.A is a hydrogen atom or a hydroxyl group; R.sup.1 is a hydrogen atom, a hydroxyl group, a thiol group, an amino group or a chlorine atom; ring J represents an optionally substituted 2-naphthyl group, or a group represented by the following general formula (II) wherein Y represents a single bond or a connecting group; ring Z represents an optionally substituted aryl group or heteroaryl group or the like; and R.sup.2 to R.sup.4, P.sup.1 and Q represents a halogen atom, a cyano group or the like.