Dust explosion hazards are always present when combustible dusts are manufactured or handled in the process. However, industries is experiencing difficulty in establishing chemical accident prevention measures because of insufficiency of information on dust explosion characteristics of combustible dust handled in industry. In this study, we investigated experimentally dust explosion characteristics of two kinds of multi-walled carbon nano tubes (MWCNT) different in particle size distribution and examined classification of dust explosion hazardous area for MWCNT manufacturing or handling process by applying the NFPA 499 code. As a result, Pmax, Kst, LEL, MIE and MIT of MWCNT 1 having 124.2 μm median diameter are obtained 6.3 bar, 56 bar·m/s, 125 g/m3, over 1000 mJ, and over 650 °C. Pmax, Kst, LEL, MIE and MIT of MWCNT 2 having 293.5 μm median diameter are 6.2 bar, 42 bar·m/s, 100 g/m3, over 1000 mJ, and over 650 °C, respectively. MWCNT 1, 2 are not categorized as combustible dust listed in the NFPA 499 Code for classification of dust explosion hazardous area because explosion severity and ignition sensitivity of MWCNT 1, 2 are below 0.35 and 0.01, respectively.