The crystal structure of the ion-exchangeable layered perovskite compounds K2La2Ti3O10 and Li2La2Ti3O10 were determined by Rietveld analysis for the powder X-ray diffraction pattern. Although the framework of the perovskite layer of lithium compound is the same as those of the corresponding sodium and potassium compounds, a fundamental difference exists. The lithium ions within the interlayer have a tetrahedral coordination because the ionic radius is too small for a rock-salt coordination. The layered perovskite compound Li2La2Ti3O10 exhibits a new phase analogous to the Ruddlesden-Popper phase.