Gas absorption accompanied by an irreversible chemical reaction of m-th and n-th order with respect to dissolving gas and reactant in liquid phase respectively, has been discussed from the viewpoints of film and penetration theories, and the approximate solutions for the reaction factor describing the effect of chemical reaction on the rate of gas absorption have been derived. These solutions were compared with the analytical and numerical solutions for the cases of some special types of reaction obtained by previous workers and the presentauthors, and were shown to give good approximation.