We have successfully synthesized a series of unique Au nanoparticles decorated hollow Pt-Pd nanoassemblies via a facial tri-block copolymer based approach for the prior formation of porous Pt-Pd nanoassemblies as the base architecture and the subsequent electrochemical treatment with HAuCl4 for fabricating extremely hollow Pt-Pd spherical shells with densely decorated Au nanoparticles. The surface-enhanced Raman scattering (SERS) performance for malachite green oxalate and pesticide such as the parathion and thiabendazole will be extensively investigated and discussed. The developed two-step polymer based approaches and the fabricated novel Au nanoparticles activated tri-metallic hollow nanoassemblies as well as their SERS performance not only provide insight of the relevant phenomena during processing and sensing, but are able to be directly applied for biochemistry, chemical analysis, food safety and environmental monitoring.