The Duchess of Portland refers to the wife or widow of a Duke of Portland, a former title in the peerage of Great Britain. The title was created in 1716 but became extinct in 1990 upon the death of the ninth Duke.

Duchesses of Portland

• Margaret Bentinck, Duchess of Portland (née Lady Margaret Harley) (1715–1785), British aristocrat, wife of William Bentinck, 2nd Duke of Portland
• Dorothy Bentinck, Duchess of Portland (née Lady Dorothy Cavendish) (1750–1794), wife of William Cavendish-Bentinck, 3rd Duke of Portland
• Henrietta Bentinck, Duchess of Portland (née Henrietta Scott) (1774–1844), wife of William Bentinck, 4th Duke of Portland
• Winifred Cavendish-Bentinck, Duchess of Portland (née Winifred Dallas-Yorke) (1863–1954), British humanitarian and animal rights activist, wife of William Cavendish-Bentinck, 6th Duke of Portland
• Ivy Cavendish-Bentinck, Duchess of Portland (née Ivy Gordon-Lennox) (1887–1982), founder of the Harley Gallery and Foundation, wife of William Cavendish-Bentinck, 7th Duke of Portland