Alexander Alcée Casamajor (1833 – 7 August 1861) was a British rower who won the Wingfield Sculls in six successive years and the Diamond Challenge Sculls at Henley Royal Regatta as well as being twice in the winning Grand Challenge Cup team.
Casamajor was an amateur and won his first public sculling match at Barnes Regatta in 1852. He rowed for Wandle Club in 1855 when he won the Wingfield Sculls and Diamond Challenge sculls at Henley beating Herbert Playford in the final. He also won Silver Goblets at Henley with Josias Nottidge beating W F Short and Edward Cadogan.
In 1856, Casamajor helped Nottidge and Playford establish the London Rowing Club, becoming secretary. As a newly founded club, they were unable to enter Henley Royal Regatta in 1856, so its members competed as members of the Argonaut Club. Casamajor was in a coxed four with Nottidge, James Paine and Playford which won the Stewards' Challenge Cup and the Wyfold Challenge Cup. In 1856 at Henley he won the Diamonds beating C Stephens in the final and partnered Nottidge again in the Silver Goblets which they won over their colleagues Paine and Playford. He also won the Wingfield Sculls for Argonaut Club.
In 1857 the London Rowing Club competed at Henley and won the Grand Challenge Cup and the Stewards' Cup with Casamajor in the crews. Though primarily a sculler, Casamajor helped the club eight win the Grand Challenge Cup at Henley in 1857 and 1859 although on both occasions he showed extreme exhaustion. He won Diamonds in 1857, beating Paine in the final.