Gas-liquid mass transfer characteristics were investigated in pressurized three-phase slurry bubble columns with variation of column diameter. Effects of gas velocity, operating pressure, liquid viscosity, solid content in the slurry phase and column diameter on the gas-liquid volumetric mass transfer coefficient(k(L)a) were determined. The effects of operating variables on the mass transfer coefficient tended to change with variation of column diameter. The mass transfer coefficient increased with increasing gas velocity or operating pressure but decreased with increasing column diameter, liquid viscosity or solid concentration in the slurry phase. The increase trend of k(L)a value with increasing gas velocity and the decrease trend of k(L)a value with increasing liquid viscosity, tended to decrease gradually with increasing column diameter. However, the effects of operating pressure and solid concentration in the slurry phase on the k(L)a value did not change considerably with variation of column diameter. The values of k(L)a were well correlated with operating variables with in this experimental conditions as k(L)a=0.02D^(-0.26)U(G)^(0.28)P^(0.43)μ(L)^(-0.04)S(c)^(-0.35)