Structural characterization and ionic conductivity properties of three members of the La1.33-xLi3xTi2O6 (being x = 0.29, 0.21 and 0.09, respectively) perovskite-type series are reported. These phases are described as tetragonal (S.G. P4/mmm) and the unit cell parameters (a approximate to 3.87 and c approximate to 7.78 Angstrom) are related to the cubic ABO(3) perovskite one. X-ray diffraction data were analyzed by the Rietveld method and an interesting feature is that the cation vacancies are concentrated on alternating A-planes (i.e. for z = 1/2) of the structure. Therefore, cation mobility seems to be due to a 2-D mechanism in such planes. Electrical properties have been measured by a.c. techniques and the higher conductivity results were obtained for the intermediate composition, x approximate to 0.21. The activation energies of the three phases are quite similar.