In this study, delay line surface acoustic wave devices were prepared using a 128° Y-cut LiNbO3 piezoelectric substrate. Pure MoS2 and composite materials of MoS2 and SiO2 with various morphologies were sprayed to form sensitive layers. By adjusting the amount of NH4OH catalyst in the precursors, the particle sizes of SiO2 nanospheres were successfully controlled at 70, 200, and 300 nm by the sol-gel method. SiO2 nanospheres were then added to the precursor for preparing rosette-shaped MoS2, and nanocomposites were synthesized by the hydrothermal method. As a result, two types of composite material were obtained, namely, the S–M structure and the M–S structure. As ammonia gas sensors, the results showed that all the sensors exhibited negative frequency shifts as the NH3 gas concentration increased. Surface area and pore size distribution analyzer (BET) analysis showed that the highest specific surface area of 115.57 m²/g occurred on the S–M structural composite material. The sensor using the S–M structural composite material has a sensitivity of 1932 Hz/ppm to NH3 gas. The sensing linearity R-squared value is approximately 0.99, with continuous dynamic sensing at NH3 gas concentrations of 5–50 ppm. Finally, we revealed that decorating MoS2 with SiO2 nanospheres can improve the adsorption of ammonia molecules and significantly enhance sensitivity.