Structural investigations of SrTiO3 thin films deposited by pulsed laser ablation onto MgO and LaAlO3 substrates are presented. The residual strain along the c -axis (the growth direction) was evaluated with conventional X-ray diffraction. Evaluation of the in-plane strain was accomplished with grazing-incidence X-ray diffraction. The unit cell of the STO film on LAO substrate had an orthorhombic structure with a coexistence of compressive strain along a -axis and tensile strain along b -axis. The film on an MgO substrate was tetragonal, stretched along the c -axis and compressed in-plane . The elemental composition of the samples was investigated using an INCA system for X-ray elemental analysis attached to a Hitachi S-4300 SEM. A comparison of the residual strain and stoichiometric ratio between as-deposited films and films annealed for four hours at 1100degreesC in flowing oxygen is presented.