Effects of homo-epitaxial LaAlO3 (LAO) layer on microstructural properties of SrTiO3 (STO) films grown on LAO substrates have been investigated. The STO films were deposited by pulsed laser deposition (PLD) on LAO (100) substrate with and without a homo-epitaxial LAO (HE-LAO) layer. The microstructure of the STO films was examined by X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). TEM and HREM studies indicate the HE-LAG layer contains a much higher density of structural defects than the LAO substrate and the STO films grown on its top. In addition, the STO films deposited with the HE-LAO layer have a reduced planar defect (boundary) density relative to those films deposited directly on the LAO substrate. The reduced planar defect density in the STO film is strongly correlated with the previously observed improvement in microwave properties of devices based on these films.