Marquess of Ailsa, of the Isle of Ailsa in the County of Ayr, is a title in the Peerage of the United Kingdom. It was created on 10 September 1831 for Archibald Kennedy, 12th Earl of Cassilis. The title Earl of Cassilis had been created in 1509 for the 3rd Lord Kennedy. This title had been created in the Peerage of Scotland in 1457. The 1st Marquess had been created Baron Ailsa in the Peerage of the United Kingdom on 12 November 1806.

Archibald Kennedy, 1st Marquess of Ailsa, KT, FRS, styled Lord Kennedy between 1792 and 1794 and known as the Earl of Cassilis between 1794 and 1831, was a Scottish peer.