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A new version of the Rietveld-refinement program RIE TAN has been developed for the analysis of angle-dis persive X-ray and neutron powder diffraction data. It has several features such as the modified pseudo-Voigt function of Thompson, Cox and Hastings, representa tion of peak asymmetry by a multi-term Simpson's rule integration, the March-Dollase function to correct for preferred orientation, and a background function con sisting of Legendre polynomials. Powder diffraction data of four inorganic compounds were analyzed with this program to test its effectiveness. In all the refine ments, the new version of RIETAN gave lower R fac tors than the old one. The result of Rietveld refinement for anatase-type Ti0. 85Sn0. 15O2 showed that the model function implemented in the new program well fits its X-ray powder diffraction pattern exhibiting anisotrop ic strain broadening.