Au–Fe₃O₄ hybrid hollow spheres have been successfully synthesized by a one-pot process via the hydrothermal treatment of FeCl₃, HAuCl₄, citrate, urea, and polyacrylamide (PAM). The amount of Au nanoparticles located in the hybrid hollow spheres can be tuned by changing the molar ratio of Au/Fe precursors. A possible synthetic mechanism of the Au–Fe₃O₄ hybrid hollow spheres has been proposed. The obtained hybrids exhibit not only a superior surface-enhanced Raman scattering (SERS) sensitivity, but also an excellent catalytic activity. The detection limit of the Au–Fe₃O₄ hybrid hollow spheres (the Au/Fe molar ratio is 0.2, Au–Fe₃O₄-0.2) for R6G can reach up to 10⁻¹⁰ M, which can meet the required concentration level for ultratrace detection of analytes using SERS. Furthermore, the catalytic experiments of the Au–Fe₃O₄-0.2 hybrid hollow spheres demonstrate that the model of 4-nitrophenol (4-NP) molecules can be degraded within 3 min and the catalytic activity can be recovered without sharp activity loss in six runs, which indicates their superior catalytic degradation activity. The reason may be due to the highly efficient partial charge transfer between Au and Fe₃O₄ at the nanoscale interface. The results indicate that the bifunctional Au–Fe₃O₄ hybrid hollow spheres can serve as promising materials in trace detection and industrial waste water treatment.