AbstractIt is found that the piezoelectric properties of glycine phosphite (GPI) were preserved up to 264 K, which contradicts the presence of a symmetry centre phase above TC. The resonance frequency jump at the phase transition was ∼0.15%, which is more than ten times smaller when compared to the sound velocity jump. In order to explain such persistent behaviour of the sample, a complementary measurement of the spontaneous polarisation Ps was made. Not only was Ps observed up to 270 K, but two kinds of polarisation were distinguished: the first disappeared at ∼226 K, and the second was present up to 270 K.