HMS Ontario can refer to several ships:

• HMS Ontario (1755), a Royal Navy schooner captured in 1756
• HMS Ontario (1780), a Royal Navy brig-sloop that sank in a storm in Lake Ontario during the American Revolutionary War and whose wreck was discovered in June 2008 between Niagara and Rochester.
• HMS Ontario (1813), a Royal Navy Cruizer-class brig-sloop ordered as HMS Mohawk and sold off in 1832.

• Ontario (disambiguation)
• HMCS Ontario
• USS Ontario