In this study, both electrical resistance tomography (ERT) and computational fluid dynamics (CFD) were employed to study the performance of the SMX static mixer in the mixing of a secondary fluid in a yield-pseudo plastic primary fluid. Using ERT, the effects of the primary fluid rheology, the primary fluid flow rate, and the secondary fluid type (Newtonian and non-Newtonian) were investigated. A CFD model was then developed for the fluid mixing in the SMX static mixer and was validated using the experimental pressure drop and the ERT mixing index measurements. Using the validated CFD flow model, the effects of the primary/secondary flow ratio and the secondary fluid viscosity on the mixing performance of the SMX static mixer were analyzed. The results from this study revealed that the SMX static mixer was effective for the mixing of highly viscous fluids especially at a lower primary/secondary flow ratio.