The surface hydrides formed on commercial purity titanium (CP-Ti) and Ti–6Al–4V alloy having been electrolytically hydrogenated in 1 N aqueous sulfuric acid solution were identified to be δ-hydrides. Structure and composition of these δ-hydrides were affected by the thermal oxide films, the additive in the electrolyte, the applied current density and the operating period. The lattice constants of δ-hydrides ( a δ) observed in this study range from 4.383 to 4.431 Å for CP-Ti and 4.293 to 4.308 Å for Ti–6Al–4V. The nonstoichiometric ratios, x, of δ-hydrides for CP-Ti after hydrogenated are not more than 1.84. X-ray diffractometry (XRD) gave a δ and x (indirectly from a δ– x curve) to characterize titanium hydrides. Glow discharge optical spectroscopy (GDOS) offered quantitative values such as maximum hydrogen diffusion depth (MHD), average hydrogen concentration ( C A), specific hydrogen uptake (SHU), hydrogen uptake efficiency (HUE), coefficients of inhibiting performance (CIP) and hydrogen absorption rates to elucidate processing parameters on the hydrogenation behavior.