A probabilistic sizing tool for rigid ceramic tiles thermal protection system (TPS) for hypersonic flight vehicles was proposed based on finite element and Monte Carlo methods. A two-dimensional probabilistic finite element model was developed, in which the uncertainties of thermal conductivities, specific heat capacities, emissivity and the thickness of TPS were considered. The temperature distributions of TPS were obtained, and the sensitivities of the input random parameters were also investigated. Based on the statistical results, the thermal reliability of ceramic tile TPS was evaluated. The numerical example indicates that the thermal reliability can be improved by increasing the thickness of ceramic tile or strictly controlling its manufacture tolerance. The proposed method could be helpful to design highly reliable TPS with minimum weight.