A uric acid biosensor aimed at a simplified determination of salivary uric acid was fabricated and utilized for measurement of diurnal variation of salivary uric acid. The biosensor measures uric acid as the change in the amount of hydrogen peroxide produced in the uricase reaction. Because uric acid is oxidized as easily as hydrogen peroxide, the osmium-HRP redox reaction was employed. The sensitivity of the biosensor was 170 nA/mM, which was sufficient for salivary uric acid determination. For the purpose of simplified measurement of a saliva sample, a paper-based saliva sampling device, which enables the sample collection regulated amount of saliva in five s, was used. As a test using an actual sample, diurnal variation of salivary uric acid was measured. The result indicated that salivary lactic acid increased in the morning. The total measurement time for the saliva measurement was approximately 3 min, which was sufficiently fast for the purpose of daily health management. The proposed method is expected to be used not only in gout treatment but also possibly in the measurement of other substances contained in saliva.