Duke of Sanlúcar la Mayor (Spanish: Duque de Sanlúcar la Mayor) is a hereditary title in the Peerage of Spain, accompanied by the dignity of Grandee and granted in 1625 by Philip IV to Gaspar de Guzmán, 3rd Count of Olivares and royal favourite to the king.

[2][3] Since the title was granted to the Count of Olivares, the first holder became popularly known as the "Count-Duke of Olivares", by conjunction of the two titles.

However, and by Royal Decree in 1882, the Countship of Olivares became officially known as the Countship-Dukedom of Olivares (condado-ducado de Olivares).

The Dukedom of Sanlúcar la Mayor remains with the original denomination, and makes reference to the town of Sanlúcar la Mayor in the Province of Seville.

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