Semyon Yakovlevich Nadson (Russian: Семён Яковлевич Надсон; 14 December 1862 – 19 January 1887) was a Russian poet.
Nadson's grandfather was a Jew who converted to the Greek Orthodox religion, his father was an official in St. Petersburg. His mother, Antonina Stepanovna Mamontova, was a Russian Orthodox, offspring of an old noble family.
Despite publishing only one book of poems (he died of tuberculosis at age 24), Nadson enjoyed a significant success, although underrated by critics for long time. His Poem "Pora" ("It Is Time" in English), was set to music by Sergei Rachmaninoff (Op.14, No. 12), and was performed by Dmitri Hvorostosky at the Ravinia Festival on 18 August 2009. It seems to have Messianic overtones.