The properties of ZnO/SiO2/Si surface acoustic wave (SAW) Love mode sensors were examined and optimized to achieve high mass sensitivity. SAW devices A and B, were designed and fabricated to operate at resonant frequencies around 0.7 and 1.5GHz. The ZnO films grown by pulsed laser deposition on SiO2/Si demonstrated c-axis growth and the fabricated devices showed guided shear horizontal surface acoustic wave (or Love mode) propagation. Acoustic phase velocity in the ZnO layer was measured in both devices A and B and theoretical and experimental evaluation of the mass sensitivity showed that the maximum sensitivity is obtained for devices with ZnO guiding layer thicknesses of 340nm and 160nm for devices A and B, respectively. The performance of the SAW sensors was validated by measuring the mass of a well-characterized polystyrene–polyacrylic acid diblock copolymer film. For the optimized sensors, maximum mass sensitivity values were as high as 4.309μm2/pg for device A operating at 0.7477GHz, and 8.643μm2/pg for device B operating at 1.5860GHz. The sensors demonstrated large frequency shifts per applied mass (0.1–4MHz), excellent linearity, and extended range in the femto-gram region. The large frequency shifts indicated that these sensors have the potential to measure mass two to three orders of magnitude lower in the atto-gram range.