The thermal stability of Ni/MgH thin film deposited on Si substrate by Unbalanced Magnetron Physical Vapor Deposition has been investigated using Ion Beam analysis (IBA) techniques. Rutherford Back-scattering Spectrometry (RBS) and Non-Rutherford Back scattering Spectrometry (NRBS) have been used to find the composition of Magnesium, Nickel and Oxygen. Elastic Recoil Detection Analysis (ERDA) has been used to determine the concentration of hydrogen at each level of heating. Heating was done in the Ultra High Vacuum (UHV) environment using a non gassy button heater. Ni/MgH sample had lost most of its hydrogen after being heated to a temperature of about 125 degree Celsius in vacuum. However, the onset temperature of hydrogen loss from the sample was found to be within 21 and 50 degree Celsius. The interface regions between the film and the substrate and between Ni and MgH layers were unaffected by this operation.