Mass transfer from single CO2 Taylor bubbles in vertical minichannels was measured for various channel hydraulic diameters D-h. The effects of channel geometries on the mass transfer were also investigated by using square ducts and circular pipes. Bubble rising velocities, v(B), in the ducts were much faster than those in the pipes due to large liquid flow areas in the corners of the ducts. The values of mass transfer coefficients in the pipes were almost the same as those in the ducts, in spite of a large difference in v(B). Sherwood numbers, Sh(D), using D-h as a characteristic length, are well-correlated in terms of the Eotvos number. The proposed Sh(D) correlation can well predict a long-term dissolution process of a Taylor bubble.