Effect of different amounts of Mg as a reductant on processing of nano-crystalline titanium diboride (TiB2) ceramic powder synthesized via self-propagating high-temperature synthesis (SHS) was investigated. Mixture of TiO2, H3BO3 and Mg powders were compacted and subjected to a hot filament on their top to SHS. Phase evolution, crystallite and particle sizes, and morphology of the products were studied by XRD, SEM, EDS and TEM techniques. Results showed that under different conditions, intermediate phases such as Mg2TiO4, Mg3B2O6, and MgTi2O5 in presence of TiB2 were synthesized. With increasing the amount of Mg, the mean crystallite size of TiB2 decreases from 36 nm in 0.8 of stoichiometric ratio to 20 nm in 1.2. Moreover, presence of diluent resulted in decreasing the crystallite size. TEM image confirm presence of agglomerated TiB2 particles with a mean particle size of 80 nm in the synthesized sample with 1.2 stoichiometric ratio of Mg.