Seongjae Yi Si-yeong (Choson'gul: ???; Hanja: ???, December 3, 1868 – April 19, 1953) was a Korean politician, independence activist, educator and neo-Confucianist scholar.
He was Vice President of South Korea from 1948 to 1951.
Yi resigned after the National Defense Corps incident of 1951.
His nickname was Seongjae (??; ??) or Sirimsanin (????; ????).
Before the Japan–Korea Treaty of 1910, he had served for Joseon as the Governor of South Pyongan Province and the President of Hansung Law Court.