The mixing performance of baffles placed with a clearance between them and the mixing vessel wall was investigated in a shear‐thinning fluid, and decolorization experiments were conducted to observe the mixing pattern under no‐baffle, standard baffle, and inner‐baffle conditions. Velocity fields were obtained by particle image velocimetry to clarify the mixing mechanism in the fluid. No isolated mixing region was seen under the inner‐baffle condition, and this condition promoted homogeneous mixing. The velocity profile clarified that the inner baffle prevented secondary circulation flow from forming an isolated mixing region and, thus, promoted homogeneous mixing in the fluid. An inner baffle with a small impeller can obtain homogeneous mixing in shear‐thinning fluids.