Copper nanocrystals have gained considerable attention for their interesting optical and catalytic activities. However, its unsatisfactory stability in humid environment limited its applications. To address this drawback, we proposed a method for coating a conformal, ultrathin gold shell on the copper nanocrystal surfaces as a protective layer. The pinhole-free ultrathin gold nano-layer should be able to protect the copper core in various environments. The successful deposition of a full gold layer relies on the introduction of a strong reducing agent to compete with and thereby block the galvanic replacement between copper and chloroauric acid (HAuCl₄), which results to pinholes on the gold layer and compromise its protective function. Significantly, the core-shell nanoparticles demonstrate good catalytic activity toward the reduction of p‑nitroaniline. Our on-going work is using shape-defined nanocrystals (copper nanocubes or platelets) to further understand the gold deposition process and improve their stability and catalytic activity. These core-shell nanocrystals have good scope for future applications in catalysis and as well as surface plasmonic effect related applications.