The relationship between crystal structure and electrochemical behavior through the lithium insertion in the perovskite oxides, LiyLa(1-y)/3NbO3 (y, = 0, 0.1, 0.25), has been investigated. The results of the relationship between the amount of inserted lithium and the number of vacancies reveal that Li+ ions insert into the vacancies at an A-site. Furthermore, observed cell potential diagrams indicate that the Li+ insertion reaction occurs stepwise. since there are two kinds of vacancy sites due to the ordering arrangement of cations in the A-site. With increasing the composition y, the extinction of electrochemical behavior due to such stepwise reaction was observed, which is attributed to the disordering of cation arrangement. Simple Coulombic calculation of electrochemical lithium insertion also supports the observed electrochemical behavior and determines the insertion step to the two kinds of vacancy sites.