Sergei Stepanovich Chakhotin (13 September 1883, Istanbul, Ottoman Empire - 24 December 1973, Moscow, Russian SFSR, Soviet Union) was a Russian biologist, sociologist and social activist of Russian origin.
He was one of the first thinkers to describe the effect of propaganda on the psychology of masses and warned against the techniques used by the Nazi Party.
He was friends with Einstein and discussed his fears concerning the rise of Nazism with him.