Recently, rare earth based hydrogen storage alloys are used as the battery negative electrode. The rate of hydriding is markedly affected by the exposure to air because the surface of metals becomes coated with oxide and hydroxide. The alkaline pretreatments is improved the surface of metals. We reported that the initial hydrogen absorption rate in electrochemical process was enhanced by heating the surface of LaNi5 in alkaline solution. In this study, we investigated the effect of KOH alkaline pretreatment on the equilibrium characteristics of the LaNi5-H system.