This article presents the transient thermoelastic behaviors of carbon/carbon composite brake disks in the brake housing during braking action. The heat transfer problem from frictional heat and the elastic problem dealing with thermomechanical deformation in brake contact are coupled to each other. The coupled heat and elastic analysis were carried out using the finite element method. The fully implicit transient scheme for the thermoelastic analysis was newly implemented to improve the accuracy of calculations at every time step. Since the heat capacity of carbon/carbon composite is very large, the high temperature of the brake disk system is confined to only the narrow regions near the friction surfaces. Therefore, the thermoelastic behaviors of carbon/carbon composite brake disk system were little affected by the thermal boundary conditions in the brake housing during braking action.