Novel lithium ion conducting oxides with perovskite structure have been synthesized and studied. It has been found that the La2/3-xLi3xTiO3 and La2/3-xLi3xNb2O6 compounds have a perovskite structure at 1/24 < x < 1/6 and 0 < x < 3/10, respectively. The results of investigating the electrical properties of both groups of perovskites indicate a high lithium ion conductivity.