In this paper, surface temperatures of ZnO arresters as a function of ambient temperatures and leakage currents were experimentally investigated. The variations of the leakage current was below 10 uA, which comes about $4.5\%$ of the normal leakage current. Temperature differences between the ambient and the surface of arresters were not shown until $150\%$ to the normal leakage current, and were remarkable over $200\%$. From the results, we deduced a couple of polynomials which enables the calculation of the leakage current by the measurement of surface temperature. Tests on used arresters have shown the same results as the experimental one. Also, we expect that an arrester diagnosis is possible by measuring the surface temperature of them after more studies on the effect of wind, moisture penetration, and arrester types.