Layered double hydroxides (LDHs) materials have shown promising behaviour in heterogeneous catalysis, and increasing the amount of exposed active sites is crucial to enhance their catalytic performance. In this work, CuMgAl-LDH@mSiO₂ nanosheets were prepared by delaminating the CuMgAl(NO₃)-LDH microcrystals followed by coating a layer of SiO₂. Structural characterizations based on SEM and BET display their slice morphology with average thickness of 5.2 nm and a large specific surface area of 244.3 m² g⁻¹. This gives rise to excellent catalytic performance toward phenol hydroxylation (conversion: 45.6%; selectivity: 97.3%). Especially, the normalized activity value is as high as 330.8 (mol phenol/mol Cu²⁺) with the efficiency of peroxide up to 91.1%. This is, to the best of our knowledge, the highest value for Cu-based heterogeneous catalysts in this reaction. This work demonstrates the unique structural feature of CuMgAl-LDH@mSiO₂ nanosheets with efficient exposure of active sites and its remarkably enhanced catalytic activity toward phenol hydroxylation.