PROBLEM TO BE SOLVED: To provide a safe xanthine oxidase inhibitor effective for treating gout and hyperuricemia.SOLUTION: A xanthine oxidase inhibitor including an extract of water caltrop is provided. An agent for suppressing the blood urate level increase that includes extract of water caltrop is also provided. The xanthine oxidase inhibitor or the agent for suppressing the blood urate level increase is safe and is useful as a drug, drink and food for treating, alleviating and preventing diseases resulting from overproduction of urate (for example, gout, hyperuricemia or the like).
