Chlorination and carbochlorination of zirconium oxide under isothermal and non-isothermal conditions along with the effects of mechanical activation on these issues were studied. Evaluation of the samples were carried out using XRD, TEM, SEM, TG, and BET techniques. The effect of mechanochemical treatment on phase transformations of monoclinic zirconia via high energy planetary ball mill at different milling times was studied. By using quantitative phase analysis through x-ray diffraction and internal standard of LiF, the most proper conditions of milling were specified at ball to powder weight ratio of 20 and milling speed of 600 rmp for balls with 20mm diameters. Mechanical treatment during the milling resulted in fine grains , increase of lattice strain , phase transformation to unstable tetragonal (t) and cubic(c). TEM and XRD studies revealed the existence of prominent amounts of amorphous phase which had been produced during milling. The decrease of specific surface estimated by BET at long milling durations reveal agglomeratio of zirconia with the help of the amorphous phase as binder. Mechanical treatment extremely increased reactivity of zirconia with chlorine gas (chlorination). Also, annealing of milled zirconia in Chlorine atmosphere resulted in formation of anionic vacancies , crystallization of amorphous phase and its transformation into cubic and tetragonal phases, and the increase of stability temperature of such phases to 800?C and 1000?C , respectively. Under these conditions, the low border energy of the grains and the existence of oxygen vacancies play an important role in the stability of tetragonal and cubic phases. By using thermogravimeter, which was designed and manufactured for the corrosive chlorine atmosphere, TG experiments were carried out for carbochlorination of zirconia in a non- isothermal way with the speed of 12 degrees per minute and chlorine flow of 60ml/min. The kinetic of carbochlorination was studied by Coats-Redfern method and it was revealed that carbochlorination of unmilled zirconium is a chemical control reaction with an activation energy of 64kcal/mol and 9/26×10 8 min -1 pre-exponential factor. Through mechanical activation of zirconium for 30, 60, and 80 hours the starting temperature of carbochlorination decreases from 912?C to 881?C, 720?C, and 620?C, respectively- the mechanism remaining a chemical control reaction. Because of activation process both the activation energy and 1 pre-exponential factor will decrease. The obtained results showed that such decreases are due to phase transformations caused by mechanical activation. In other words, reactivity of tetragonal and cubic phases which have been formed by mechanochemical process is more than that of monoclinic phase.