Carbon dioxide was absorbed into benzene solutions of PB (polybutene) and PIB (polyisobutylene) in an agitated vessel to get the liquid-side volumetric mass transfer coefficient (k(L)a). The effect of liquid-phase viscosity, pseudoplasticity, and viscoelasticity of the benzene solutions of PB and PIB, and speed and size of impeller on the gas-liquid mass transfer have been investigated. The elastic properties, considered in the form of the Deborah number, were found to decrease the volumetric mass transfer coefficient. On the basis of experimental data of k(L)a, a dimensionless equation for k(L)a was proposed by using the Deborah number.