The thermochemical properties of rare earth Invar alloys were investigated by using a high temperature calorimeter. The enthalpies were measured in two temperature ranges. 350 similar to 750K for Y2Fe14B, NaFe8.8V3.2, SmFe10V2, YFe10V2 and 550 similar to 950K for La2Fe14B, Ce2Fe14B, Nd2Fe14B, Sm2Fe14B, NdFe12-xVx (x-1.6, 2.0, 2.4, 2.8). The relationships between temperature and enthalpies as well as heat capacities were determined, influence of heat capacity with the Invar properties was analysed.