The elastic, piezoelectric, and dielectric constants of single‐crystal BaLaGa3O7, which belongs to the 4¯2m class of the tetragonal system, were measured. The six independent elastic constants, two piezoelectric constants, and coupling coefficients were determined using standard resonance‐antiresonance measurements and the following results were received (cijin 1011 N/m2):c11=1.78,c12=1.03,c33=1.17,c13=0.88,c44=0.39,c66=0.54,e14=0.29 C/m2,e36=0.10 C/m2,kl14=0.141, andkl36=0.055. The two dielectric constants were measured at low frequency using a three electrode configuration. The relative values of these constants were determined to be &egr;T11/&egr;0=12.7, &egr;S11/&egr;0=12.4, &egr;T33/&egr;0=9.5, &egr;S33/&egr;0=9.5.