This study reports the results of investigations carried out to determine the Curie temperature (Tc) of various homogenized praseodymium-based alloys represented by the formula: Pr14Fe79.9-xCo16B6Nbx (where x = 0, 0.01, 0.05, 0.1, 0.15, 0.50). The influence of niobium content on the microstructure of these alloys has investigated. The Curie temperature decreased about 3 °C for x = 0.5 at. %. It has been observed a remarkable grain refinement on the microstructure of the Pr14Fe79.8Co16B6Nb0.1 alloy when compared to the niobium-free alloy (x = 0 at. %).