Au　coated　magnetic　polyphosphazene　(MPCTP)　composite　particles　(MPCTP@Au)　were　fabricated　with　sensitive　SERS　activity.　The　MPCTP　particles　were　generated　by　coating　polyphosphazene　on　Fe3O4　nanoparticles　through　precipitation　polycondensation　of　hexachlorocyclotriphosphazene　and　phloroglucinol.　MPCTP@Au　composite　particles　were　obtained　by　deposition　of　Au　nanoparticles　on　MPCTP　by　the　reduction　of　HAuCl4.　The　size　and　the　thickness　of　the　Au　shell　can　be　controlled　by　varying　the　amount　of　HAuCl4.　The　magnetic　core　endowed　the　composite　particles　with　good　magnetic　responsiveness,　which　allowed　the　analyte　to　be　enriched　and　separated　from　the　complex　matrix,　and　significantly　simplifying　the　sample　pretreatment　procedure.　The　SERS　activity　of　MPCTP@Au　composite　particles　were　evaluated　by　DTNB　as　model　Raman　reporter,　and　the　limits　of　detection　(LOD)　of　DTNB　was　10-8　mol/L.　A　high　efficient　SERS　immunoassay　system　based　on　the　MPCTP@Au　substrates　for　the　detection　of　immunoproteins　was　developed.　Human　IgG　and　rabbit　IgG　were　quantitatively　determinated　simultaneously　by　this　immunoassay　system.　The　quantitative　determination　of　the　immunoglobulin　G　(IgG)　was　achieved　and　the　LOD　of　human　IgG,　rabbit　IgG　and　the　mixture　of　human　IgG　and　rabbit　IgG　were　as　low　as　10　fg/mL,　100　pg/mL　and　1　ng/mL,　respectively.　The　results　showed　that　the　MPCTP@Au　composite　particles　have　broad　application　prospects　as　high　performance　SERS　active　substrates　for　immunoprotein　analysis.　©　2023　Elsevier　Inc.