Mass transfer coefficient at the annular outer wall of a double tube bubble column was experimentally measured using a slurry of fine glass beads with mean diameter 26 mu m. Mass transfer coefficient was obtained by means of an electrochemical redox reaction system. Mass transfer behavior of the solid liquid system is similar to that of a liquid single phase. Mass transfer coefficients were increased by approximately ten times by bubbling. Major factors affecting the mass transfer at the annular wall for the gas-liquid and the gas-liquid-solid systems are the gas holdup and the properties of liquid or slurry.