Wave motions appear on the surface of a single-bubble rising in liquid when the bubble Reynolds number exceeds a certain critical value. Such wave motions enhance the mass transfer from the bubble to the liquid especially under the condition that the bubble surface is contaminated by surfactant. This is caused by surface renewal due to the wave motions. The mass transfer coefficient under this condition was experimentally measured using a simplified model. Water and CO₂ gas were used as the working fluids. Two empirical equations for the mass transfer coefficient were proposed.