Gas holdup, bubble behavior, interfacial area and gas-liquid mass transfer in a 5 m internal-loop airlift reactor with non-Newtonian fluid were studied in the superficial gas velocity (U-g) range of 2-12 cm/s. Air and aqueous CMC solutions of 0-0.45 wt% were used as the gas and liquid phases, respectively. It was found that increased Ug or CMC concentration led to a wider bubble size distribution and an increase in the bubble Sauter diameter. The volumetric mass transfer coefficient increased with an increase in U-g and a decrease in CMC concentration. In the air-water system, k(l)a/alpha(g) was found to be independent of U-g and was 0.21/s, and a constant liquid-side mass transfer coefficient (k(l)) was found in the heterogeneous regime. However, in the air-CMC solution system, the influences of the superficial gas velocity and liquid viscosity were much more complicated: k(l)a/alpha(g) was not constant and was affected by the superficial gas velocity and CMC concentrations; the interfacial area increased with an increase in U-g and a decrease in CMC concentration; k(l) increased more significantly with increasing U-g, and no obvious trend was found for the influence of CMC concentration on k(l). (c) 2010 Elsevier B.V. All rights reserved.