Cao Guojiu (Imperial Brother-in-law Cao); whose real name was Cao Yi and courtesy name was Jingxiu; is a Chinese mythological character and one of the Eight Immortals. Better known to his contemporaries as Cao Jingxiu; Cao Guojiu is believed to have been a descendant of Cao Bin; a general of the early Song Dynasty; and the younger brother of Empress Cao; wife of Emperor Renzong of the Song Dynasty.

Cao's younger brother Cao Jingzhi abused his imperial connections to engage in corrupt practices; leading to his brother trying to change him; with little success. Cao Guojiu also used his family's wealth to help the poor and balance his brother's misdeeds. After his brother was caught and accused by Imperial offricials for his misdeeds; Cao was so ashamed that he gave up his office and retired to the countryside as a recluse. He then met the immortals Zhongli Quan and Lu Dongbin; who taught him Daoist magical arts and helped him become immortal.

Cao Guojiu is often depicted in official imperial robes and holding a jade tablet or castanets. He is often recognised as the patron deity of acting and theatre.