In order to estimate the strain energies of pure Cu and pure Al prepared by ECAP and ARB processes, dislocation densities remaining in these metals after each process were analyzed by the Warren-Abervach method based on the Williamson-Hall plot from a series of data taken by conventional X-ray diffractometry. The measured dislocation density was higher by several times in pure Cu than in pure Al regardless of ECAP and ARB, resulting in the higher strain energy stored in pure Cu than in pure Al. Also, the dislocation density was found to be lower in the f.c.c. phase in pure Cu than that in the lath martensite phase in high Cr ferritic steels. Furthermore, it was observed that the amount of stored strain energy in pure Al depended considerably on its purity.