Mark Andreyevich Natanson (Russian: Марк Андреевич Натансон; alias - Бобров, or Bobrov) (25 December 1850 (N.S. 6 January 1851), Švenčionys - 29 July 1919, Berne) was a Russian revolutionary and one of the founders of the Circle of Tchaikovsky, Land and Liberty, and the Socialist-Revolutionary Party. In 1917, he was a leader of the Left Socialist-Revolutionaries, supporting the Bolsheviks in the October Revolution. He was the uncle of Alexander Berkman.