Piezoelectric ReCa4O(BO3)3 (ReCOB, Re: rare earth) crystals, including ErCOB, SmCOB, PrCOB and LaCOB, were successfully grown by the Czochralski (Cz) method. The dielectric constants were determined to be ε11 T/ε0 = 9.50, ε22 T/ε0 = 11.8 and ε33 T/ε0 =9.80 for ErCOB, ε11 T/ε0 = 9.70, ε 22 T/ε0 = 13.9 and ε33 T/ε0 = 9.90 for SmCOB, ε11 T/ε0 = 9.60, ε22 T/ ε0 = 15.3 and ε33 T/ε0 = 10.0 for PrCOB, ε11 T/ε0 = 9.40, ε22 T/ε0 = 15.0 and ε33 T/ε0 = 9.60 for LaCOB, respectively. The electromechanical coupling factors k26 and piezoelectric coefficients d26 were found to be 18.5% (7.6 pC N -1), 27.0% (12.7 pC N-1), 31.5% (15.8 pC N-1) and 25.0% (11.8 pC N-1) for ErCOB, SmCOB, PrCOB and LaCOB crystals, respectively. The dielectric and piezoelectric properties as a function of Re3+ ion radius were studied, with maximum values being observed in the PrCOB crystals, due to the similar ion radius of Pr3+ and Ca 2+. The relationship between the structure and dielectric/ piezoelectric properties of ReCOB crystals was explored, to further optimize the dielectric and piezoelectric properties in ReCOB series crystals. © 2011 IOP Publishing Ltd.