YCa4O(BO3)3 (YCOB) crystal was reported to be a potential material for high temperature piezoelectric sensing applications. In this paper, the full matrix of electro-elastic constants, including dielectric permittivities, elastic constants, and piezoelectric coefficients were determined. The relative dielectric permittivities were measured to be , , , and , respectively. The piezoelectric coefficients were determined to be d11 = 1.7, d12 = 3.9, d13 = −4.2, d15 = −1.1, d24 = 4.4, d26 = 7.9, d31 = −0.77, d32 = −2.5, d33 = 1.4, and d35 = −5.0 pC N−1. In addition, piezoelectric cross-talks of YCOB crystals were investigated, where (XZlw)45°/35° and (YXt)−30° crystal cuts were found to possess pure thickness shear mode, with relatively large effective piezoelectric coefficients, being on the order of d15 = 8.8 and d26 = 9.0 pC N−1, respectively.