An experimental study for estimation of thermal contact conductance between an exhaust valve and its seat in an internal combustion engine has been accomplished. In this study, an actual exhaust valve and its seat are utilized in a setup. Several experiments under different conditions have been conducted to acquire desired data. In addition, an inverse heat conduction problem for estimating both constant and periodic thermal contact conductance has been solved using the conjugate gradient method (CGM) with adjoint problem for function estimation, which converges very rapidly and is not as sensitive to the measurement errors. The influence of the contact pressure upon the thermal contact conductance is investigated by using valve springs with different stiffness. The results show that the thermal contact conductance increases as the stiffer valve spring is used. The results obtained with CGM and the linear extrapolation ones are in good agreement.