Many different sizes of activated carbon fixed beds are widely used for adsorption of organic solvent vapors and hazardous gases, such as air cleaners, gas masks and gas sampling tubes, but only limited information is available for the comprehensive relationship between adsorption characteristics of the fixed bed and practical factors; the amount of activated carbon, the gas flow rate, the vapor concentration and the bed diameter. The authors investigated experimentally the effect of these factors on the adsorption zone length, the effective adsorption capacity and the breakthrough time. The following results were obtained; 1) The adsorption zone length was approximately independent of the amounts of activated carbon packed in a column of a definite diameter. Therefore, the effective adsorption capacity increased with the increasing activated carbon amount, and the breakthrough time was nearly proportional to it. 2) The adsorption zone length increased and the effective adsorption capacity reduced with the increasing gas flow rate. 3) The adsorption zone length was little affected by the vapor concentration, but the effective adsorption capacity increased with the increasing concentration. 4) In case of the same amount of activated carbon, the adsorption zone length, the effective adsorption capacity and the breakthrough time reduced with the increasing bed diameter.