The autunite-meta-autunitel—meta-autunite II series was studied by x-ray diffraction. In America and Europe, autunite is usually found as the meta-autunite I phase, whereas in Japan it occurs as autunite. By studying the process by which autunite is dried and heated until it finally forms a high temperature phase, the writer has determined the diffraction pattern of each phase. Single crystals were analyzed by the Weissenberg method, and the lattice constants and space groups were determined. The large cell proposed by Donnay and Brichard for meta-autunite was not found. Meta-autunite II is orthorhombic, with a0=6.55, bo = 7.05 and co = 8.16 Å. This co value is smaller than the co of meta-autunite I, contrary to the values hitherto reported.