Rubber is used in important functional parts such as automobiles.Polar rubbers such as NBR and ACM, which provide excellent heat and oil resistance are used in automobile parts.A common issue with polar rubber is mechanical properties at low temperature. Plasticizers are added in such polar rubber to improve flexibility at low temperature. Plasticizers for rubber are required to keep heat resistance, oil resistance and cold resistance.Rubber is selected depends on applications. Suitable plasticizer is also selected depending on the applications. This article explains the basic characteristics of rubber plasticizers and how we select plasticizer for rubbers in each application.