HMS Mermaid was a 24-gun sixth-rate post ship of the Royal Navy, built in 1748–49, which served in the Seven Years' War.

Mermaid was ordered on 4 February 1748, with the contract being awarded to Henry Adams, of Bucklers Hard, with the keel being laid on 2 April.

She was built to a design by the Surveyor of the Navy Joseph Allin, named Mermaid on 6 December, launched on 22 May 1749 and completed on 7 August 1749 at Portsmouth Dockyard, having cost £4,211.16.7d to build, and with a further £3,829.3.11d spent on fitting her out.

She refitted and underwent repairs over the next few months, and recommissioned in January 1754 under Captain Washington Shirley, sailing for New England in July 1754.

[1] She bilged on a sandbank off Big Grand Cay in the Bahamas on 4 December 1759 and was abandoned as a wreck on 6 January 1760.