Abstarct In this paper, effect of mechanical activation on microwave reactive sintering of MgO - TiO2 system was investigated. Mixtures of MgO and TiO2 were milled at different times. Mixed powders along with 10 h milled powders were chosen for microwave sintering between 1000- 1400⁰C. Results showed that increasing of temperature up to 1400̊C for mixed powders could not give rise to complete formation of Magnesium titanate phases and raw materials were in the products. Also the densities of these samples were about 3 g/Cm3. With milling of reactants up to 10 h, it seems reactions could be completed at 1000⁰C and the density was augmented to 3.58 g/Cm3. The samples were sintered at 1400⁰C in a microwave furnace exhibited good microwave dielectric properties while εr and tan δ were 16.3 and 0.0001 respectively.