This paper aims to investigate the effect of silicone oils as processing agent affecting the loss and recovery of hydrophobicity. The recovery of hydrophobicity was evaluated by the measurement of the surface electrical resistivity and the contact angle on the SIR surface. Two kinds of silicone oils (1 and 2) having different molecular weight were selected under a consideration of hydrophobicity and processability. SIR specimens were exposed to corona discharges in air and the specimens were analyzed with contact angle and surface resistance measurements. It was observed that the contact angle and the surface resistivity of SIR increase gradually with testing time. The fast recovery of hydrophobicity of SIR, expressed by the increment of contact angle and surface resistivity, was showed in SIR2 containing silicone oil 2.