Metallic samples subjected to heating-cooling cycles present Thermal Residual Strain. X-ray diffraction tests showed that the samples after the cycles change in line-profile width. By increasing the maximum cycle temperature, at first, a profile broadening occurs relative to the width observed before the cycles, then a narrowing, when the temperature overcomes a certain value that is proper of each metal. An accurate analysis of the diffraction line profiles was performed on copper samples in order to distinguish the effect on the line width produced by the crystallite size with respect to that produced by residual stresses. At first, our analysis was restricted to one reflection from a (hkl) plane, so, a single-line method for the analysis of X-ray diffraction line width was adopted. Then, the methods for line profile analysis, in which two orders of reflection are considered, were also applied and the experimental results are presented together with those obtained with one reflection.