We have prepared new perovskite-type lithium ion conductors, LaxMyLi1-3x-yNbO3 (M = Ag and Na) and investigated the lithium ion conductivity in these compounds. Maximum lithium ion conductivity at 300 K was found to be 3.9 x 10(-5) 8 . cm(-1) for La0.25Ag0.20Li0.05NbO3, which contain the minimum amount of Li ion among these compounds. This result indicates that the Li ion conductivity of these compounds is mainly dominated by the activation energy. The reason for low ionic conductivities of these compounds is that the lattice parameters are not sufficiently optimized for Li ion conduction in the perovskite niobate.