The thermal stability of electroless Ni-X-P alloys is important for many applications in the electronics industry. This property of amorphous Ni-P and Ni-Cu-P alloys prepared using two different methods (melt-spinning technique and electroless deposition) is compared by differential scanning calorimetry. Analysis of the crystallization kinetics in both cases is carried out and its parameters are determined. Rapidly quenched alloys show higher thermal stability, while the total heats of crystallization are equal for both preparation methods. It is shown that the introduction of copper into electroless deposited Ni-P alloys exerts two favorable effects : an increase in crystallization starting temperature and a decrease in magnetization of the ferromagnetic phase precipitated after annealing.