As a way to clarify the causes for deterioration of sulphur dioxide adsorption capacity of active carbon, the environmental conditions which bring deterioration to active carbon were investigated. The results indicated that exposure to oxygen at a temperature level of around 300°C gives large influence on sulphur dioxide adsorption capacity of active carbon.Consequently, the relationship among the degree of activity for sulphur dioxide, concentration of oxygen in the atmosphere, temperature of the gas, and exposure time to oxygen was investigated. The results clarified that all these factors are related to deterioration of the degree of activity.Then, regeneration method of the deteriorated active carbon was studied, that is, the deteriorated active carbon was heated at 300∼800°C in the various surrounding gases.After this treatment, change in sulphur dioxide adsorption capacity of active carbon was investigated. It was clarified that the deteriorated active carbon is regenerated nearly to the initial capacity of original active carbon when heated at 550°C and 730°C respectively in the hydrogen stream and the other gases.