For improving the thermal conductivity of carbon nanotube-epoxy composite, we have performed the chemical surface pre-treatment of multi-walled carbon nanotube (MWCNT) and investigated its effects. In the experiments, the mixtures of nitric and sulfuric acid have been used as the surface modifier for MWCNT. The chemical surface pre-treatments by acid mixtures lead to the production of oxygen-containing functional groups on the surfaces of MWCNT. Also, the surface area and pore volume of acid-treated MWCNT (AT-MWCNT) become larger than those of pristine MWCNT. By actions of the chemical pre-treatment, AT-MWCNT is well dispersed and forms the heat flow network in epoxy matrix, resulting in higher thermal conductivity of carbon nanotube-epoxy composite.