Polymer insulating materials such as epoxy resin have been using in the distribution and transmission lines as outdoor insulator. Several advantages of using epoxy resin are its low density, better dielectric properties and it has higher volume resistivity than glass and ceramic. However, some weaknesses of epoxy resin are easily influenced by environmental factors such as humidity, ultraviolet radiation, acid rain and effect of contamination. Consequently, surface of insulator will easily damage due to electrical tracking which is indicated by surface tracking. To improve the dielectric properties such as hydrophobic contact angle then silicon rubber was compounded. In this paper to understand of silicon rubber influence on leakage current characteristics and hydrophobic contact angle of epoxy resin insulating materials have been analyzed. The tests were conducted using the Inclined-Planed Tracking (IPT) method according to IEC 60587:1984 standard with Ammonium Chloride (NH4Cl) as contaminant. Flow rate of contaminant was 0.3 ml/min and high voltage AC 3.5 kV 50 Hz was applied to the top electrode. The experimental results reveal that the hydrophobic contact angle, leakage current and surface degradation depend on the composition of silicon rubber. Silicon rubber was improving epoxy resin performance as insulator. Based on analysis it is found that epoxy resin with silicon rubber without silica sand offers the optimum surface tracking and erosion resistance. We conclude that silica sand doesn’t influence on leakage current characteristics.