Mass transfer coefficients between particles and liquid in the region of high particle concentration were obtained by the use of both active and inert particles suspended in solid-liquid two-phase upflow through vertical tubes and in stirred tanks. When adding inert particles of low density such as polystyrene and anion-exchange resin beads, mass transfer coefficients decreased with increasing particle concentration, remarkably above concentrations from 20 to 30%. Meanwhile, the coefficients increased in two-phase tube flow and decreased in stirred tanks when using glass beads. The experimental results were correlated with parameters including (1) the kinematic viscosity of slurry and (2) the effective energy dissipation rate, based on the concept that only a part of the energy supplied contributes to the mass transfer. The first method was successfully applied only to the system containing low-density particles, and the second to systems having either high- or low-density particles. The effectiveness of energy dissipation on mass transfer at high particle concentration is discussed in some detail.