HMS Nereus was a 46-gun modified Leda-class fifth-rate frigate built for the Royal Navy during the 1810s.

She was never commissioned and was converted into a store ship in 1843 for service in South America.

[2] Nereus, the second ship of her name to serve in the Royal Navy,[3] was ordered on 24 April 1817, laid down in January 1819 at Pembroke Dockyard, Wales, and launched on 30 July 1821.

[4] She was completed for ordinary at Plymouth Dockyard 22 August–12 September 1821 and the ship was roofed over from the mainmast forward.

By December 1856, the ship was stationed in Callao, Peru, but had returned to Valparaíso by 1 August 1863.