Large single crystals of lead potassium niobate were grown by the method of pulling from a melt, and their piezoelectric properties were preliminarily investigated. The crystals have ferroelectric tungsten bronze structure with a Curie point of about 460°C. Spontaneous polarization lies perpendicular to the c axis as in ferroelectric PbNb2O6. Particularly large electromechanical coupling factors were measured; i.e., 0.69 ± 0.03, 0.73 ± 0.03, and 0.59 ± 0.01 for k15, k24, and kt, respectively. Temperature coefficients of the fundamental resonant frequencies in y‐ and z‐cut plates were found to be <30 ppm around room temperature.