Grain refinement of Ti-6Al-4V alloy can be achieved by eletrolytic hydrogenation and subsequent vacuum annealing. The depth of grain refinement increases with increasing hydrogen uptake. Cathodic charging was performed at various current densities and periods in1N H2SO4(subscript (aq)) with or without adding thiourea and its derivatives. The results analyzed by using X-ray diffractometry (XRD) and glow discharge spectrometry (GDS) show that hydrogenation performance is lower for the specimens charged with the addition of thiourea. This may partly arise from the properties of the additives and partly from those of hydrides fromed at the specimens surface during cathodic charging.