In general, internal cells are required to solve thermo-elastoplastic problems using a conventional boundary element method (BEM). However, in this case, the merit of BEM, which is the easy preparation of data, is lost. The conventional multiple-reciprocity boundary element method (MRBEM) cannot be used to solve the elastoplasticity problems, because the distribution of initial strain or initial stress cannot be determined analytically. In this paper, it is shown that two-dimensional thermo elastoplasticity problems can be solved without the use of internal cells, by using the triple-reciprocity boundary element method and a thin plate spline. Initial strain and initial stress formulations are adopted and the initial strain distribution is interpolated using boundary integral equations and a thin plate spline. A new computer program was developed and applied to several problems.