The electrochemical characteristic of boron-doped polycrystalline diamond thin film electrodes with 4 mm×4 mm in size was studied using cyclic voltammetry and potentio-static method. The potential windows all are - 500- + 800 mV in the electrolyte solution of 0. 1 mol/L KC1, NaNO3, NaOH and KH2PO4+Na2HPO4(pH = 6. 86), but -200- + 1100 mV in 0.1 mol/L H2SO4 and HC1. The oxide peak potential of K[Fe(CN)6] is +500 mV, and similar to that of Pt electrode. The response current is proportional to the square root ...