Carbon nanotube/mesoporous silica composites with controlled diameter and bundle size have been synthesized by using highly selective catalytic method. The composites were characterized by SEM and TEM. Results suggest that the bundle size, rather than the nanotube diameter or differences in work function, is more important in determining the field emission properties of SWNT/mesoporous silica composites. The possibility of tailoring the electrical properties of SWNT emitters by adjusting the synthesis parameters has been demonstrated. In addition, the present results show that the as-produced SWNT/mesoporous silica composites have similar or better field emission properties than the purified nanotube samples, even though the concentration of nanotubes on the emitting surface of the as-produced was much lower than that in the pure SWNT sample. The good field emission efficiency of the as-produced material combined with the convenience of eliminating any purification process make this material an attractive field emitter. Thus we can anticipate that the method presented in this work offers a solution to forming the bi-component structure of nanomaterials