Polymer melt temperature dependence on the pressure have been measured directly by a novel temperature sensor in a versatile test rig which was developed to measure melt temperature profiles in the injection moulding processing. The results show that the melt temperature increases linearly with the pressure applied to it. The larger the initial bulk melt temperature, the larger the temperature rise for a particle rise in pressure. The temperature rise resulting from compression is also related to the structure properties of the polymer.