An incremental theory is presented for solving the problem of elastoplastic thick-walled tubes subjected to transient thermal loading. The effective stress in a thick-walled tube subjected to thermal loading is shown by examples that it is not a monotonic function with respect to the radius, but is strongly dependent upon the history, gradient, and distribution of the temperature in the tube. The multiple elastic-plastic boundary problem of a thick-walled tube can be solved by use of the presented theory. Because temperature history is included in the analysis, the theory is particularly suitable for predicting stress and strain distributions, and locations of the elasticplastic boundaries of a thick-walled tube subjected to transient-state thermal loading.