Mg_xTi_1-xO composite oxides were prepared via the sol-gel method with magnesium acetate and tetrabutyl titanate as precursors. Ni was dispersed on these Mg_xTi_1-xO composite oxides with varying x by using wet impregnation method. The Ni/ Mg_xTi_1-xO catalysts were characterized with ICP-OES,X-ray powder diffraction, N₂ adsorption, FT-IR, H₂-TPR and TEM. Over prepared Ni/ Mg_xTi_1-xO catalysts, tri-reforming (simultaneous oxygen-carbon dioxide-steam reforming) of methane for its conversion into synthesis gas (H₂ and CO) with desired H₂/CO ratio (1.5~2.0) has been investigated in a fixed bed flow reactor under atmospheric and pressurized conditions. Changes in interactions between metal and support by varying x were discussed and correlated to the catalytic properties. Over 95% CH₄ conversion and about 90% CO₂ conversion can be achieved in tri-reforming over Ni catalysts supported on Mg_xTi_1-xO at 850°C and 1 atm. The nature of support, the interaction of metal-support, and the interaction of CO₂ with support play an important role in tri-reforming of CO₂ conversion in the presence of H₂O and O₂. The Ni catalysts supported on the composite oxides with x of about 0.7 turned out to be far more resistant to carbon formation. This may be related to the decoration of metal surfaces with Mg_0.7Ti_0.3O species. This Mg_0.7Ti_0.3O destroys the large ensembles of metal atoms that serve as active sites for carbon deposition. In addition, composition of feed stocks also has an impact on mitigation or elimination of carbon deposition.