SiO2@Co3O4 core–shell nanorattles with different Co3O4 shell thicknesses have been successfully synthesized by the calcination of SiO2@α-Co(OH)2 at 500 °C. The synthetic approach is facile, economical, and requires no surface modification. The synthesized materials were thoroughly characterized using powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric analysis (TGA), Brunauer–Emmett–Teller (BET) analysis, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and diffuse reflectance spectroscopy (DRS). SEM analysis indicates a hierarchical core–shell morphology for SiO2@Co3O4 and the TEM results indicate the core–shell nanorattle morphology. Diffuse reflectance spectroscopy studies indicate that the SiO2@Co3O4 core–shell nanorattles show two absorption bands in the range 420–450 nm and 700–750 nm related to ligand to metal charge transfer transitions (O2− → Co2+ and O2− → Co3+). The SiO2@Co3O4 core–shell nanorattles act as an artificial peroxidase enzyme mimic with enhanced intrinsic peroxidase-like activity compared to pure Co3O4 nanoparticles and horseradish peroxidase (HRP), a natural enzyme. The SiO2@Co3O4 core–shell nanorattles show higher kcat and kcat/Km values compared to pure Co3O4 and HRP indicating their applicability as an artificial enzyme mimic in biomedicine and bio-sensing.