We report the effects of Sr or Ba substitution on the crystal growth and electrical and mechanical properties of Ca₂Al₂SiO₇ (CAS) piezoelectric single crystals, which are suitable for use in high-temperature pressure sensors. Ba was scarcely incorporated in the crystal lattice of CAS. Strontium-substituted CAS single crystal with a nominal chemical composition Ca_0.75Sr_1.25Al₂SiO₇ (CSAS125) was grown by the Czochralski method. Although the piezoelectric modulus d′₃₁ of CSAS125 is a bit lower than that of the CAS crystal, the rupture strength of the (XYt)45° rotation cut substrate of CSAS125 crystal was 170 MPa, which was 1.2 times higher than that of CAS crystal. By considering the rupture strength and the apparent piezoelectric d^*₃₁ coefficient calculated for the crystal rotation cut of CAS crystal, the CSAS125 crystal substrate with a rotation cut of (XYt)25° was found to indicate a rupture strength of 220 MPa and a piezoelectric d′₃₁ coefficient of approximately 2 pC/N.