Microstructural and analytical investigations have been used to describe the competing mechanisms,of aluminotherrriic and borothermal reduction of titanium oxide in the presence of molten aluminum and boron. This study indicates that the reaction proceeds through complex non-equilibrium reactions. A multistage reaction model, is proposed to describe the process by the TiO2 surface is reduced to form Al2O3 andTiB(2). Al2O3 and TiB2 are formed by a series of aluminothermic and borothermic reactions. To investigate the proposed surface-controlled reaction model, the effects of powder particle size on-formation of reinforcing phases, and microstructural evolution-have been investigated. Small-sized TiO2 powder promoted the formation of the reinforcing phases at lower temperatures, and the resultant reinforcing particulates exhibited smaller sizes, Which is in good agreement with theoretical predictions.