Nanosize Nickel ferrite (NiF) was synthesized by the co-precipitation methods and its effect as a 5 % by mass additive was studied on the thermal decomposition of micrometer and nanometer size NTO. In the presence of 5 % NiF additive, the thermal decomposition peak temperature of NTO was decreased from 276.36 to 260.18 oC and that of nano NTO was decreased from 261.38 to 258.89 oC (β=10 oC min-1). The kinetics parameters confirms the catalytic activity of NiF for the thermal decomposition of NTO, and nNTO as the parameters such as activation energy (NTO=~25.45 % and nNTO=~45.94 % decrement), and pre-exponential factor (NTO=~21.94 % and nNTO=~43.12 % decrement) were decreased when 5 % NiF additive was added to NTO, and nNTO. The rate of the decomposition process was increased in the presence of 5 % NiF catalyst, indicating the faster thermal decomposition of both NTO, and nNTO in the presence of nickel catalyst.