Hydrogen atoms have been doped into La 2 - x Sr x CuO 4 (0.1 ≤ x ≤ 0.25) at a fairly low temperature of 140°C, in order to suppress the removal of lattice oxygen atoms by a reduction reaction in H 2 atmosphere. The hydrogen and oxygen contents of hydrogenated samples are determined by means of H-NMR measurements and thermogravimetric analyses, With a period of the hydrogenation, the a-axis is slightly elongated while the c-axis is almost unchanged. The hydrogenation results in significant decreases in the volume fraction of superconductivity although T c -values remain unchanged.