<p>In this study, a composite of CsPbBr₃@PbBr(OH)@Ag as the surface-enhanced Raman scattering (SERS) substrate was developed to realize the rapid, sensitive, and selective detection of 4-mercaptopyridine (4-MPY). This composite was prepared based on a strategy involving the CsPbBr₃ quantum dots (QDs) encapsulated in PbBr(OH) with the microbrick framework by using the in situ chemical reduction method. And then the silver (Ag) nanoparticles were conjuncted with CsPbBr₃. This is the first time that the composite of CsPbBr₃@PbBr(OH) has been utilized in conjunction with silver (Ag) nanoparticles for 4-MPY SERS detection in aqueous solutions. CsPbBr₃ and Ag nanoparticles could synergistically enhance the SERS signal of the analyte, and PbBr(OH) could passivate the surface defect sites of CsPbBr₃ nanocrystals, reducing the impact of ion migration that causes instability, thereby protecting the nanocrystals from interference in aqueous environments. After 7&#xa0;days of refrigerated storage, the CsPbBr₃@PbBr(OH)@Ag composites still exhibited about 70% SERS detection capability, confirming their ability to overcome the instability of perovskite quantum dots in water. The adsorption behavior of 4-MPY on the CsPbBr₃@PbBr(OH)@Ag composites was studied using typical SERS spectral bands, and these were contrasted with the SERS spectra on pure silver nanoparticle substrate which was prepared by the same method without CsPbBr₃@PbBr(OH). The limit of detection (LOD) of the composite is 17.56&#xa0;ng/L, considerably lower than that of the pure Ag substrate. The enhancement mechanism is attributed to the synergistic effect of the metal’s localized surface plasmon resonance (LSPR) and the charge transfer (CT) mechanism in the perovskite. This method indicates significance in facilitating the rapid detection of 4-MPY and advancing the application of perovskite in SERS.</p>