Ammonia is a harmful atmospheric pollutant that poses serious threats to human health and ecological environment. Therefore, the development of low-energy, high-performance and real-time ammonia monitoring system is imperative. In this study, p-aminobenzene sulfonic acid (pABSA) modified MoO₃/polypyrrole (PPy) composite materials were successfully prepared using an in situ chemical oxidation polymerization method with MoO₃ and pyrrole monomer (Py) as raw materials and FeCl₃ as an oxidant, along with pABSA as an anionic surfactant. Microstructure of the materials was characterized to explore influence of pABSA-modified MoO₃/PPy composite materials on the gas sensing performance. The results demonstrate that at room temperature, the response value of pABSA-modified MoO₃/PPy composite material to a mass concentration of 1×10⁵ µg/L ammonia is 188%, which is ~8 times higher than that of pure PPy (22%), exhibiting excellent selectivity and stability. The enhancement in sensing performance can be attributed to the formation of a heterojunction between MoO₃ and PPy as well as surface modification by pABSA leading to increased mobile charge carriers on the material's surface.