Microstructural characterizations on the (1-x)La-2/3-TiO3.xLaAIO(3) (LTLA) system were conducted using transmission electron microscopy. The presence of La2Ti2O7 and La4Ti9O24 phases in pure La2/3TiO3 is confirmed by the electron diffraction pattern. When x = 0.1, the ordering due to the A-site vacancies could be confirmed by the presence of antiphase boundaries (APBs) and 1/2(100) superlattice reflection. As x increases, the ordering decreases and finally disappears when x = 0.6. The tilting of oxygen octahedra could be demonstrated by the presence of the ferroelastic domains in the matrix and (111) and 1(110) superlattice reflections in selected area electron diffraction patterns. In pure LaAIO(3), only the antiphase tilting of oxygen octahedra is present due to the presence of 1/2(111) superlattice reflection. In the LTLA system of x = 0.1, both the antiphase and in-phase tiltings of the oxygen octahedra are involved; however, in the range of x from 0.3 to 0.9, the antiphase tilting of oxygen octahedra has appeared. The growth of the ferroelastic domains is influenced by the APBs in the matrix.