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Abstract Viscosity measurement has recently captured considerable attention due to its wide range of applications in fields such as pharmacy, food industry, cosmetic industry, and biomedical diagnostics. Acoustic wave sensors such as quartz crystal microbalance (QCM) are well-known mass sensors that also show their capability in measuring liquid viscosity. However, the challenges for QCM-based viscosity measurement devices lie in their low sensitivity and unstable response. Herein, we report an ultrasensitive micropillar-enabled acoustic wave (μPAW) viscometer by fabricating well-defined polymethyl methacrylate (PMMA) micropillars on a QCM substrate to achieve ultrahigh sensitivity for liquid viscosity with a stable response thanks to a unique vibration coupling between the micropillar and QCM substrate. The μPAW based viscometer shows a 20-fold improvement in the measurement sensitivity over traditional QCM viscometers and achieved an excellent limit of detection (LOD) while measuring the viscosity of sucrose liquid as low as 0.054 wt%. The microdevice developed in this work is a promising tool for the viscosity measurement of liquids.