Abstract Single crystals of potassium titanyl phosphate (KTP) are grown by the flux method and characterized by XRF, IR absorption spectrometry, and plasma emission spectroscopy. Lattice parameter variation with temperature is studied by powder X-ray diffraction. The difference (a-2b), which is a measure of the pseudo-tetragonality of the lattice, is observed to decrease to a value close to zero at 324 K, and increase again for higher temperatures. Calorimetric measurements have indicated a specific-heat jump at the same temperature. This jump is observed to have a strong dependence on the rate of change of temperature. Dielectric measurements on single crystals in the frequency range 0.01 – 100 kHz indicate a change in the frequency dependence of tanδ 33 at 324 K. These observations probably indicate crossover behaviour, the origin of which may be in the change of the superionic character of KTP at 324 K.