Here, we describe quantitative analysis of plasma uric acid (UA) levels using an improved HPLC-UV method, which provides highly sensitive analysis using microliter volumes of plasma. Phosphoric acid aqueous solution (pH 1.8) was used as the mobile phase. The quantitative analysis of oxypurines in plasma using a polymeric-ODS with high-carbon content (ca.17%) column (Φ4.6×250mm) was accurate and reproducible. The reproducibility of the UA analysis had a determination limit of 0.14mg/dL and a coefficient of closing variation of 0.98%. The results by our method confirmed that the plasma UA levels were increased in mice with oxonic acid-induced hyperuricemia compared to normal mice, and that allopurinol reduced the plasma UA levels in these mice. This method allows the measurement of plasma uric acid levels using small plasma samples.