Linear scan voltammograms of various concentrations of AA and UA was used to test the effect of screen-printed carbon electrode (SPCE) and oxygen plasma-treated SPCErsquos (OP-SPCE) ability to distinguish the oxidative peak potentials (Epa) of UA from AA. The oxygen plasma-treated SPCE (OP-SPCE) could make the oxidative peaks of ascorbic acid (AA) and uric acid (UA) on the linear scan voltammograms became more defined with the Epa to 150 mV (RSD =6.9%,n=7) and 350 mV (RSD =0.6%, n=7), respectively. While measuring a composite solution containing of AA and UA, the AArsquos current signals, generated at the shoulder of the AA peak curve on the linear scan voltammogram caused interference behavior thereby background currents presented to the uric acidrsquos oxidative peak. The degree of background was found proportional to the concentration of AA in the composite solution with a linear regression equation of y = 0.0226x + 2.421 (R2=0.9962). A sequential measurement of ascorbic acid and uric acid concentration in a composition solution by linear scan voltammograms on the plasma treated screen-printed carbon paste electrode has developed: (1) determined the AA concentration (2) determined the degree of interference caused by AA at the uric acidrsquos oxidative peak (3) the estimated interference-free UA peak current is determined by subtracting the level of AA interference. By using the fitting procedure, The UA concentration can be quantitatively and accurately analyzed. Excellent recovery rates (97.9 to 106%) and RSD of 1.4% were obtained for the measurement of UA, even in the presence of high concentrations of AA.