•The ferroferric oxide/polystyrene/silver particles with a well-defined core–shell structure have been synthesized.•The composite particles provide excellent SERS performance and have a detecting limit of 10−10 M R6G.•The composite particles show superior stability and reproducibility for SERS application. A novel Ag-coated Fe3O4@Polystyrene core–shell microsphere has been designed via fabrication of Fe3O4@Polystyrene core–shell magnetic microsphere through a seed emulsion polymerization, followed by deposition of Ag nanoparticles using in-situ reduction method. Such magnetic microspheres can be utilized as sensitive surface-enhanced Raman scattering (SERS) substrates, using Rhodamine 6G (R6G) as a probe molecule, with both stable and reproducible performances. The SERS detection limit of R6G decreased to 1×10−10 M and the enhancement factor of this substrate on the order of 106 was obtained. In addition, owing to possessing excellent magnetic properties, the resultant microspheres could be separated rapidly by an external magnetic field and utilized repeatedly for three times at least. Therefore, the unique renewable property suggests a new route to eliminate the single-use problem of traditional SERS substrates and will be promising for the practical application.