 Guidobaldo married Elisabetta Gonzaga, the sister of Francesco II Gonzaga, Marquis of Mantua.Guidobaldo was impotent, and they had no children, but Elisabetta refused to divorce him.He fought as one of Pope Alexander VI's captains alongside the French troops of King Charles VIII of France during the latter's invasion of southern Italy; later, he was hired by the Republic of Venice against Charles.