The oxidation kinetics of nickel nanoparticles having an approximate mean diameter of 15.5 nm was studied here. Conversion data were derived from both thermogravimetric analysis (TGA) and X-ray diffraction (XRD) analysis in the temperature range of 280 similar to 350degreesC. The results were consistent with each other and found to be modeled well by the equation based on core-shell diffusion controlled kinetics. Oxidation rate constant of nickel nanoparticles were fitted for these temperatures and its activation energy was found to be about 32.4 kcal/mol. The resulting Arrhenius expression of rate constant is k (cm(2)/s) = 9.33 x 10(-5) exp (-32.4 (kcal/mol)/RT).