Sancho Alfónsez (or Adefónsez) (ca.

1093 – 29 May 1108) is the only son of Alfonso VI of Castile and León and his heir from May 1107, eventually co-ruling from Toledo.

He predeceases his father, being killed while trying to escape the field of the Battle of Uclés.

His death, on his first recorded military expedition, precipitates a succession crisis that ends with the accession of his elder half-sister Urraca and her husband, Alfonso the Battler, already King of Navarre and Aragon, to the throne of Kingdom of Castile-León.