To further enhance the sensing properties of metal oxide semiconductor, the combination with some metal sulfide will be an effective method. In our research, the heterostructures of MoO3 nanobelts and PbS nanoparticles were successfully synthesized through simple and less expensive wet chemical routes. The microstructure, morphology, and chemical composition of MoO3@PbS nanocomposites were analyzed by various characterizations. Compared to the pristine MoO3 nanobelts, MoO3@PbS nanocomposites-based sensor exhibited higherresponse and quicker response/recovery rates to triethylamine (TEA). The limit of detection is better than 0.4 ppm, and the response time and recovery time were only 2 s and 10 s, respectively. The significantly improvement of TEA sensing properties is attributed to the combination of changing electronic structures and p–n heterojunctions. The present PbS nanoparticles-functionalized MoO3 nanobelts could be a promising candidate for the practical application to selectively detect TEA vapor.