Doping effects of Sr and/or Mg on the crystal structures of LaGaO3 perovskites were investigated. The doping with Mg into Ga-site in LaGaO3 led to structural change from the orthorhombic primitive lattice (Pbnm) to the orthorhombic body-centered lattice (Ibmm) at room temperature. The orthorhombic cell (Ibmm) of LaGa0.9Mg0.1O2.95 changed to the monoclinic (I2/a) by doping with Sr into La site. Neutron powder diffraction analyses revealed that these compounds had GaO6 octahedral tilt. The GaO6 octahedral tilt angles were reduced with doping with Sr and/or Mg.