Thermal expansion coefficients for Sr- and Mg-doped LaGaO3 were measured and the doping effect was discussed in terms of the content of oxygen vacancy. The thermal expansion coefficients of the oxides became large with dopant content. A large shrinkage caused by the phase transition from orthorhombic to rhombohedral for LaGaO3 was observed at 421 K. The shrinkage became small and broad with Sr and Mg doping. The transition temperature became higher with the Mg content in the case of Mg doping. The theoretical calculation of the thermal expansion coefficient of these oxides was also conducted and the calculated thermal expansion coefficient of LaGaO3 was in good agreement with the experimental one except for the temperature range of the phase transition. The larger thermal expansion coefficients due to Sr and Mg doping were ascribed to smaller binding energy in the oxides by the presence of oxygen vacancy using the theoretical calculation.