The performance of gas-liquid mixing processes in mechanically agitated vessels is commonly expressed in terms of the degree of gas dispersion. In fact, the local measurement of mixing parameters provides a more accurate description of the mixing effectiveness, especially for systems containing non-Newtonian fluids. For instance, the fluid flow of complex yield-pseudoplastic solutions is highly affected by the local shear stress, leading to non-homogeneous air distribution throughout the mixing vessel. Coaxial mixers, in turn, have demonstrated energy-efficient characteristics for the non-Newtonian fluids that improve the mixing homogeneity due to the independent rotation of a central impeller and a close-clearance impeller. Therefore, the objective of the present work is to investigate the axial profile of the local gas holdup in a PBT-anchor coaxial mixer containing xanthan gum solutions, which is a biopolymer widely utilized as an emulsion stabilizer, dispersing agent, and thickener. The rheological behavior of the solutions was described by the Herschel-Bulkley model, and the effect of the xanthan gum concentration on the gas holdup distribution was analyzed. Electrical resistance tomography (ERT) was employed to obtain the gas holdup from the conductivity measurements of the mixture in each of the four horizontal planes. It was observed from the results that the volume fraction of the gas phase increased downwards for all biopolymer solutions. Furthermore, a decrease in xanthan gum concentration reduced both the non-homogeneity in the gas distribution and the overall gas volume fraction. In contrast, the larger viscosity gradient resulting from higher xanthan gum concentration enhanced the gas holdup in high shear stress regions, whereas the air dispersion distant from these regions was weakened due to the higher viscous forces.