Structure refinements of solid solutions of (Ca1−xSrx)TiO3 (x = 0.0, 0.25, 0.5, 0.6, 0.65, and 1.0) were undertaken using single crystals at ambient conditions. Their lattice constants, c/a axial ratios, and cell volumes indicate continuous changes from orthorhombic to cubic through a tetragonal phase. The orthorhombic structure is continuous between x = 0.0 and x = 0.6, and a phase at x = 0.65 shows a tetragonal structure with space group I4/mcm. With increasing Sr substitution, the symmetry changes to cubic with Pm3̅m space group. A-O and B-O distances in ABO3 perovskite were determined as a function of the composition of the A cation (Ca and Sr). Tilting and rotation angles of the TiO6 octahedral linkage with x of (Ca1−xSrx)TiO3 were also evaluated. Single-crystal structure refinements of Ca0.35Sr0.65TiO3 perovskite at 3.5, 4.1, and 7.0 GPa at 300 K were carried out using a diamond anvil cell. The tetragonal phase transforms to an orthorhombic structure with space group Pbnm at 3.5 GPa. The polymorphic transition of VIIIA2+VIB4+O3 perovskites under compression is discussed.