1919 Polish coup attempt in Lithuania

1919 Polish coup d'état attempt in Lithuania
Date August – September 1919 Location Kaunas, Lithuania Result Coup discovered, Polish plotters arrested by Lithuanian authorities
Belligerents
Polish Military Organization, Lithuanian branch	Lithuania
Commanders and leaders
Józef Piłsudski Leon Wasilewski Tadeusz Kasprzycki Stanisław Narutowicz Jurgis Aukštuolaitis	Mykolas Sleževičius
Casualties and losses
Many PMO members in Lithuania arrested, 117 put on trial

The Polish coup d'état attempt in Lithuania refers to a failed attempt by Polish Chief of State Józef Piłsudski to overthrow the existing Lithuanian government of Prime Minister Mykolas Sleževičius, and install a pro-Polish cabinet that would agree to a union with Poland. The Polish intelligence agency, the Polish Military Organization (PMO), was to carry out the coup d'etat, planned to be implemented in August 1919. The coup was designed to seem to be an initiative by local Lithuanians aiming to free their government of German influence. The PMO hoped to rely on the assistance of sympathetic Lithuanian activists. They were thwarted by the lack of cooperation and the unwillingness of sufficient number of Lithuanians to support the Polish cause.

After the Sejny Uprising, a Polish revolt against the Lithuanian authorities in one of the disputed border regions, Lithuanian intelligence intensified its investigation of the Polish minority and sympathizers in Lithuania, and uncovered the planned coup. The Lithuanians, not knowing the membership of the PMO, arrested numerous Polish activists and destabilized the PMO network enough to prevent the coup attempt. Later the full membership list was obtained and the PMO in Lithuania was dissolved. The coup further strained Polish–Lithuanian relations.