We have studied the effect of physical and chemical properties of α-alumina on the catalytic cracking of naphtha at atmospheric pressure in the temperature range 800-880 ℃ and LHSV range of naphtha 3-10 hr-1. Catalytic effect of alumina on the activity and selectivity for the naphtha cracking was investigated, and the performance of catalytic cracking with alumina was compared with that of thermal cracking. The ethylene and propylene yields increased 10% and 2%, respectively, in naphtha cracking in the presence of α-alumina compared with the non-catalytic thermal cracking at the same experimental condition. However, the selectivity toward ethylene and propylene was about the same for both non-catalytic thermal cracking and catalytic cracking on the α-alumina. The enhancement in the ethylene and propylene yields can be attributed to both the enhanced heat transfer from the reactor wall to the reactant through α-alumina acting as a heat transfer medium and “the surface effect” of the alumina enhancing the formation of the radical. We observed the difference in the ethylene yield by 3 wt% depending on the pore characteristics of α-alumina. It was found that the α-alumina having large pore openings of several tens of μm or higher is favorable in catalytic cracking of naphtha. We ascribe the result to the fact that in such large pores, the mass transfer resistance is less and the pore blocking by coking progresses slowly. That is, the naphtha cracking would take place in the large pores more effectively compared to the small pores and as a result, the higher ethylene yield would be expected in naphtha cracking in the presence of the α-alumina having larger pore openings.