Corona discharge is affected by various factors such as vapors and so on. Humidity is familiar vapor and understanding its effect to corona discharge is important to realign stable condition. Siloxane is known as one of most influential vapors to corona discharge stability. On the condition of corona discharge in the atmosphere containing siloxane vapor, the voltage to maintain corona discharge current constant is monitored as a function of time. The increase of the voltage is observed when the siloxane vapor is sent to the discharge area and the decrease of the voltage is observed just after stopping siloxane vapor mixing. From the increase and the decrease of the voltage, main mechanisms of the voltage change are considered as wire degradation and discharge restraint by siloxane vapor itself in corona discharge.