The temperature dependence of the complete set of elastic, dielectric, and piezoelectric constants of KTiOPO 4 single crystal has been measured from 20 C to 150 C. All 17 independent constants for the mm2 symmetry piezoelectric crystal were measured from one sample using extended resonance ultrasound spectroscopy (RUS), which guaranteed the self-consistency of the matrix data. The unique characteristics of the RUS method allowed the accomplishment of such a challenging task, which could not be done by any other existing methods. It was found that the elastic constants (c E 11 , c E 13 , c E 22 , and c E 33) and piezoelectric constants (d 15 , d 24 , and d 32) strongly depend on temperature, while other constants are only weakly temperature dependent in this temperature range. These as-grown single domain data allowed us to calculate the orientation dependence of elastic, dielectric, and piezoelectric properties of KTiOPO 4 , which are useful for finding the optimum cut for particular applications.