Thermodynamic properties of mechanically alloyed Ni and Al powders were analyzed using differential scanning calorimetric after different durations of mechanical alloying. Results show an increase in stored enthalpy in the alloyed powders with increase in mechanical alloying duration. The temperatures at which Ni3Al intermetallic compound formed were lowered when milling time was prolonged. After 300 minutes of mechanical alloying, a transition reaction from disordered fcc to ordered Ll2 of intermetallic compound was observed. X-ray diffraction patterns also confirmed the formation of Ni3Al intermetallic compound after that time. Further mechanical alloying was found to lower the transition temperature which was related to the increase in stored energy.