It has become important to consider global environmental issue. In order to reduce fuel consumption of automobiles, development of low rolling resistance tires has been promoted. They are mostly made of rubber compound filled with silica. Rubber temperature control in mixer has become more important, because silica mixing, with silane coupling reaction, needs to be under constant temperature for better mixing quality. Mixer temperature is controlled by water cooling of chambers and rotors. There have been some qualitative approaches about mixer cooling. However, quantitative prediction of rotor cooling would be still little. Heat conduction analysis of rotor, under steady and unsteady condition, had been carried out to investigate rotor cooling of internal type mixer. The results of unsteady analysis were mostly accorded with experimental results, and heat release rates from rotors in operating conditions were predicted by steady analysis. In the future, this analysis could be applied for design of different shape rotor or scale up of mixer and be coupled with flow analysis in mixers or structural analysis of rotors.