The acetaldehyde adsorption capacities of activated carbons impregnated with various amines were experimentally studied by using fixed beds. It was found that the adsorption capacity of impregnated activated carbons is influenced by the steric structure of impregnants as well as their acidity. For activated carbons impregnated with aromatic amines, ortho and meta substituents on the benzene ring hindered the condensation reaction with acetaldehyde. The activated carbon impregnated with aminobenzenesulfonic acids differed from that impregnated with the other amines in the acetaldehyde adsorption mechanism in that a Doebner-Miller reaction was involved. Also, aminobenzenesulfonic acids were not only the reactant but also the acid catalyst in the removal of acetaldehyde. Since p-aminobenzenesulfonic acid reacts with acetaldehyde without steric hindrance in the Doebner-Miller reaction, it is the most suitable impregnant for the chemisorption of acetaldehyde.