Cellulose nanocrystal (CNC) gold nanoshell was prepared using a polymer-coated CNC as a template. A seed-mediated shell growth approach (ex situ) was employed, gold nanoparticles (AuNPs) of two sizes were prepared, and the effect of the size of AuNP on the shell quality (smoothness, evenness, and continuity) was elucidated. Additionally, a novel one-pot synthesis approach (in situ) was evaluated for the preparation of the gold nanoshell, where polymer-coated CNCs with adsorbed ascorbic acid were used to reduce Au ions to form a metallic gold shell on CNC. The surface coverage was manipulated by adding different amounts of plating solutions. The formation and morphology of gold nanoshells were evaluated by zeta potential measurements, dynamic light scattering, UV-vis spectroscopy, and transmission electron microscopy (TEM). The catalytic performance of the CNC-gold nanostructures for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) was governed by the surface area of gold shells.