SF6 is designated as special reduction gas in the Kyoto Protocol because of its high GWP (23,900 times that of CO2). In Japan, the volume of SF6 emissions is decreasing in spite of increasing SF6 production in recent years. To develop thermal decomposition technology for surplus SF6 and to study the apparent SF6 decomposition rate, we investigated fundamental data such as the rate constant and activation energy of SF6 decomposition using a tube reactor. It was found that SF6 decomposition in both He and Ar base gases was a first-order reaction with respect to SF6 concentration. Activation energy of SF6 decomposition was 354 and 371 kJ . mol(-1) in He and Ar base gas, respectively. The rate-determining step of SF6 decomposition was the gas phase reaction.