<p>The rapid development of biosensors has driven significant advancements in thickness-shear (TSh) film bulk acoustic resonators. The mode-coupling vibrations of a multilayered TSh ZnO FBAR sensor with a tilted <i>c</i>-axis in the piezoelectric thin film are investigated in this study. The dispersion curves for bulk wave propagating in the ZnO FBAR sensor are derived, and general mode-coupling solutions are constructed by superimposing wave solutions of several eigenmodes along both positive and negative propagation directions. These solutions are then substituted into the higher-order stress-balanced principle to derive the frequency spectral relations, enabling prediction of mode-coupling behaviors in the TSh FBAR sensor. The effect of the <i>c</i>-axis tilting angle on mode coupling is analyzed using displacement distributions of vibration modes. Numerical results show that the <i>c</i>-axis tilting angle induces changes in frequencies and propagation wavenumbers in the larger wavenumber regions of the dispersion curves, leading to significant shifts in the frequency spectral curves along both the length-to-thickness ratio and the frequency axis. Optimal structural parameters are identified from the frequency spectra to avoid strong mode coupling and terrible structural design. This study provides fundamental insights into mode-coupling control and structural design for FBAR sensors in liquid environments.</p>