This paper describes the developed method for predictions of transient internal surface temperatures and heat-flux obtained from thermocouples, which are installed through the wall of the rocket motor nozzle. Heat-Flux was estimated by using the prediction of internal surface temperatures from numerical solutions of the inverse heat conduction problem (IHCP). Three Heat-Flux gauges are manufactured and used in convergent, throat, and divergent sections. The temperatures are measured with starting operation of the rocket motor along the gauges where the thermocouples are connected to the data acquisition system interfacing with the PC. The measured unsteady temperature behavior is approximated by polynomials third degree in space and time. The measurement results indicate that the maximum reading temperatures are at the throat section. No differences in time were appearing in curves to reach maximum prediction surface temperatures.