Mass transfer and mixing performances are very critical for xanthan gum fermentation process. Power consumption, local and average volumetric mass transfer coefficient (k L a) were compared for six impeller combinations in a 50L perspex tank with xanthan gum solutions. Impellers used in various combinations can be distinguished as two categories: “small-diameter” impeller, which include Rushton turbine, hollow blade turbine and wide-blade hydrofoil impeller and “large-diameter” including ellipse gate impeller, Intermig and double helical ribbon. The results show that in order to gain the same power input, the rotating speed of “small-diameter” impeller combinations increases as the concentration of xanthan gum increases, while it decreases for “large-diameter” impeller combinations. The two categories also show distinguished mass transfer rates. For the “small-diameter” impeller combinations, the k L a values near the wall region drop faster than that in other areas as the concentration of xanthan gum increases. While for the “large-diameter” impeller combinations, the distribution of k L a is homogenous except in the bottom area but with poor gas dispersion capabilities as concentration of xanthan gum increases. The averaged k L a for each impller combination was correlated well with the specific gassed power input, superficial gas velocity and effective viscosity. The obtained correlation shows that the k L a strongly depends on specific power input and viscosity, but is less influenced by the gas flow rate.