The paper presents estimated thermal expansion coefficients of 316SS and 508LAS base, 316SS filler or similar metal weld (SMW), and 316SS-508LAS dissimilar metal weld (DMW) filler and butter weld metals. These base and weld metals are typically used in nuclear reactor pressure boundary components. Accurate estimation of the expansion coefficients of these metals is essential for accurate estimation of thermal-mechanical stress in reactor pressure boundary components. In this paper we present the expansion coefficients of 316SS and 508LAS base, 316SS-SMW filler, and 316SS-508LAS DMW filler and butter weld metals. The coefficients were estimated based on our own experimental data. The corresponding expansion coefficient results and the FE validation results are presented in this paper. We anticipate that these types of results can be used as guidelines for choosing appropriate expansion coefficients for thermal-mechanical stress analysis of safety critical nuclear reactor components.