This paper describes a method of coating metallic gold (Au) nanoparticles with chitosan (CS) shells in an aqueous solution. A colloidal solution of Au nanoparticles with a particle size of 16.5 ± 1.7 nm was prepared by reducing the Au ions (III) with sodium citrate in water at 80 °C. CS coating was achieved in an aqueous solution containing the Au nanoparticles by using CS as a shell source and sodium hydroxide as a pH adjuster at 25 °C. Ultraviolet-visible extinction spectroscopy and transmittance electron microscopy observation revealed that the Au nanoparticles were coated with CS shells. Additionally, the CS shell thickness could be varied in a range up to 2.2 nm by changing the CS concentration during the CS-coating process. [Figure not available: see fulltext.].