Grand Duke Sergei Alexandrovich Romanov (April 29, 1857 - February 4, 1905, Old Style) was a 5th son of Emperor Alexander I of Russia. A Poruchik of the Leib Guard, he took part in Russo-Turkish War of 1877-78, was consequently promoted to Colonel.
In 1884, married Elizabeth of Hesse (Yelisaveta Fyodorovna ), the dauther of Ludwig IV of Hesse and sister of Alexandra Fyodorovna.
Promoted to Major General in 1887 and made Colonel-in-Chief of the Preobrazhensky regiment of the Leib Guard. On February 26, 1891, he was made Adjutant General of the Svita and assigned Moscow Governor General. Made a member of the State Council in 1894. Promoted to Lieutenant General and assigned Commander of Moscow military district in 1896. He supported the police-run trade unions of Colonel Zubatov. Resigned from Governorship on January 1, 1905 but continued as Commander of Moscow military. Was killed while on service in Kremlin by Socialist-Revolutionary Kalyayev.