The theoretical analysis on the selectivity of gas-liquid reaction is developed by taking into account the role of mass transfer based on the film theory. The reaction scheme considered is represented as follows: (B(liq.) +A(gas)) → R(liq.), (R(liq.) +A(gas))→S(/iq.). The rate of conversion and the relation between the yield of the intermediate product and the conversion are presented for a semibatch reactor and a continuous stirred tank reactor. It is shown that various reaction conditions such as the ratio of the rate of reaction to that of mass transfer, and the concentration of gas and liquid components have considerable effects on the selectivity.