Petrograd Seimas (Lithuanian: Rusijos lietuvių seimas Petrograde or Visos Rusijos lietuvių seimas) was a conference of Lithuanian activists in Petrograd, Russian Republic, held on 9–16 June [O.S. 27 May – 3 June] 1917 to discuss the political future of Lithuania. Citing the right of self-determination, the delegates discussed whether Lithuania should seek autonomy or full independence. While it failed to unite Lithuanian activists, it helped to crystallize ideas on Lithuania's independence.
The February Revolution brought political freedoms and Lithuanians hurried to organize their political parties. There was a need to organize an authoritative political body that could represent all Lithuanians and work towards obtaining autonomy or full independence from Russia. Representatives of five Lithuanian parties established the Council of the Lithuanian Nation (Lietuvių tautos taryba) in February 1917. To boost its authority and recognition, the council called the Petrograd Seimas attended by 334 deputies. There were passionate disagreements between the political right (Party of National Progress, Lithuanian Christian Democratic Party) and left (Popular Union of Lithuanian Socialists, Social Democratic Party of Lithuania) both on procedural questions and fundamental issues. The left advocated for autonomy within Russia while the right advocated for full independence. When the right won by a narrow margin of votes, the socialists withdrew in protest.
Such splintering of the Lithuanian movement brought an end to the Council of the Lithuanian Nation and Lithuanians were unable to gain any kind of recognition or acknowledgement from the Russian Provisional Government before it was toppled in the October Revolution. Political initiative was taken over by Lithuanians in German-occupied Lithuania when they organized Vilnius Conference and elected the Council of Lithuania in September 1917.