High-quality and large piezoelectric single crystals of Pb[(Zn1/3Nb2/3)(0.91) Ti0.00]O3 (PZNT91/09) fabricated by the Bridgman method were investigated regarding the material constants and their temperature dependence. The single crystals poled along [00 1] of the original cubic direction possess high piezoelectric constants such as g(33) and g(31), as well as high dielectric constant epsilon(33)(T)/epsilon(0) (4600), electromechanical coupling factor of the k(33) mode (95.3%) and d(33) (2500 pC/N). In particular, since k(31) and d(31) reach 80.8% and - 1700 pC/N, respectively, the crystals can be applied for use in sensors and actuators with high performance. Based on the temperature dependence, we inferred that there is a relatively large difference in the elastic compliance (s(11)(E)) between rhombohedral and tetragonal phases. The cause of the high piezoelectricity in rhombohedral PZNT91/09 single crystals is thought to be the mechanical softness which leads to easy deformation by the poling field in comparison with the tetragonal phase.