The objective of this work was to investigate electric submersible pumps performance within polymer-laden (non-Newtonian) fluid conditions. The study focuses on the pump performance derating, mechanical shearing of polymer molecular chains in the pump, and the applicability of existing correlations. Two different ESPs (82 stages and 7 stages) were tested in a newly-build Pump Testing Facility. The measurements included pressure, flow rate, torque, rotational speed, and temperature. First, the pump’s experimental water performance under constant intake pressure and constant rotational speed were compared to the manufacturer's catalog curves. The obtained performance was then used as the basis for the viscous experiments. Additionally, fluid samples were taken during all tests and were subsequently analyzed. The experiments were conducted for three polymer concentrations and three rotational speeds. The tests showed that the performance derating factors are much higher than expected, although a low viscous fluid was present. Most likely, the non-Newtonian fluid behavior was responsible for this substantial performance loss. Moreover, also the startup torque is significantly higher for the polymer-laden liquid. Mechanical shearing of the molecular polymer chains was minor. The fluid conditions present during the experiments might have affected these observations. Lastly, when comparing the experimental performance data with existing correlations, it can be said that they do not hold for the non-Newtonian fluid pumped. The novelty of those experiments was the testing of a powerful 82-stage electric submersible pump using a non-Newtonian fluid, in order to investigate the pump performance and fluid shearing effects.