In this study, a novel viscosity measurement technique based on measuring the deflection of flexible (poly) dimethylsiloxane (PDMS) micropillars is presented. The experimental results show a nonlinear relationship between fluid viscosity and the deflection of micropillars due to viscoelastic properties of PDMS. A calibration curve, demonstrating this nonlinear relationship, is generated, and used to determine the viscosity of an unknown fluid. Using our method, viscosity measurements for Newtonian fluids (glycerol/water solutions) can be performed within 2–100 cP at shear rates γ = 60.5–398.4 s⁻¹. We also measured viscosity of human whole blood samples (non-Newtonian fluid) yielding 2.7–5.1 cP at shear rates γ = 120–345.1 s⁻¹, which compares well with measurements using conventional rotational viscometers (3.6–5.7 cP). With a sensitivity better than 0.5 cP, this method has the potential to be used as a portable microfluidic viscometer for real-time rheological studies.