This study reports a controlled route for straightforward synthesizing novel microporous nanocomposites of ZIF-8 type metal-organic frameworks material incorporated with multiwalled carbon nanotubes (MWNTs). The prepared ZIF-8/MWNTs samples were characterized by XPS, XRD, SEM, TEM, N-2 adsorption and TGA experiments to investigate the effects of synthesis methods on the formation of the hybrid composite structure of ZIF-8 nanocystals growing on MWNTs. The ZIF-8/MWNTs nanocomposites were successfully synthesized by the method of adding MWNTs into a zinc nitrate solution prior to react with a 2-methylimidazole solution and the microporous structures of the ZIF-8/MWNTs nanocomposites were controlled by the MWNTs content. As an adsorbent for adsorptive removing benzoic acid (BA) from water, the prepared ZIF-8/MWNTs-25 (B) nano-composite exhibits the best adsorption capacity of 303 mg/g, about 65 mg/g higher than the ZIF-8. The improvement in the BA adsorption is due to the pore/size-selective BA adsorption of the effective micropores yielded by the ZIF-8/MWNTs hybrid composite structure, in addition to the basic-acid, coordination, and pi-pi stacking interactions between ZIF-8 and BA. The high adsorption capacity and good reusability of the ZIF-8/MWNTs-25 (B) nanocomposite suggests that it can be applied as novel adsorbents showing attractive potential.