Marquess of Castelldosrius (Spanish: Marqués de Castelldosríus) is a hereditary title in the Peerage of Spain, accompanied by the dignity Grandee and granted on 6 April 1696 by Charles II to Manuel de Oms y Santa Pau, knight of the Order of Malta, governor of Tarragona, viceroy and captain general of Mallorca, of Peru, of Tierra Firme and of Chile.

[1] The grandeeship was merged into the marquessate on 9 July 1701 by Philip V, later confirmed on 1 May 1703.

[3] The heir apparent is Tristán Jerónimo Ramírez Ruiz de la Prada (eldest son of the 13th Marchioness).

However, Ágatha Ruiz de la Prada, niece of the 11th Marquess, sued his uncle, the 12th Marquess, for the Marquessate of Castelldosrius and the Barony of Santa Pau, both of which had claim by him, on the grounds that she was the rightful heir to the said titles, as her mother was older than Santiago, and thus, in accordance with a law passed in 2005, she was next in line to both titles.

[6] After almost 4 years of legal battles, Ruiz de la Prada, through judicial sentence, was granted both titles.