Active transition metal species (Co, Mn, Ni, Fe, or Cu) supported on a chemically modified SBA-15 silica were prepared as heterogeneous catalysts. The heterogeneous liquid phase oxidation of p-xylene on the prepared catalysts was carried out to investigate the possibility of the development of heterogeneous process for easier catalyst separation. The Co species bound on the SBA-15 (Co-SBA-15) was found to be the most effective for the oxidation to corresponding aromatic carboxylic acids than the other transition metal species. In addition, the effects of reaction variables such as reaction time (0.5 ~ 9 h), reaction temperature (130 ~ 190 ℃), total pressure (10 ~ 25 atm) and the partial pressure of oxygen (1 ~ 9 atm) were studied on the Co-SBA-15 catalyst. At high levels of conversion, the considerable catalytic activities to p-toluic acid were observed, even though formation of terephthalic acid, an solid product, was very low and then the catalyst was easily deactivated due to build-up of solid products on active sites. The proposed reaction network based on the selectivities of intermediate oxidation products for p-toluic and terephthalic acid was similar to that on the homogeneous Co/Mn catalytic reaction system. This indicates that the Co-SBA-15 catalyst is a heterogeneous catalyst which can behave like a homogeneous catalyst and may be well applied to the liquid phase oxidation of hydrocarbons without formation of solid products.