A lead-free ferroelectric (Bi,K)TiO 3 (BKT) was synthesized by a hydrothermal process and characterized systematically at various temperatures. Well-crystallized BKT in the tetragonal phase was identified at a hydrothermal temperature over 220°C. Small cubic particles were observed, regardless of hydrothermal temperature. The BKT sintered at 1050°C was observed to be a typical relaxor behavior and very stable against frequency and temperatures, respectively. The sintered-BKT ceramics exhibited a high temperature of maximum dielectric permittivity (T max =356°C at 10 6 Hz) with piezoelectric constant (d 33 =65pC/N) and electromechanical coupling factors (k p =0.22, k t =0.43). Thus, the sintered-BKT showed excellent temperature stability with a high-T max and piezoelectric properties.