The temporary capital of Lithuania (Lithuanian: Laikinoji sostinė) was the official designation of the city of Kaunas in Lithuania during the interwar period. It was in contrast to the declared capital in Vilnius, which was part of Poland from 1920 until 1939. Currently, the term temporary capital, despite being factually out of date, is still frequently used as a nickname for Kaunas, the second largest city in Lithuania.
Lithuania refused to have diplomatic relations with Poland until the ultimatum of 1938. Railroad traffic, telegraph lines and even mail could not cross the Polish–Lithuanian border. Lithuania continued to refer to Vilnius as its capital in all official documents, including the constitution. Since that city was controlled by Poland, all Lithuanian authorities and military command were transferred to Kaunas, which became the seat of the government.[4] To reconcile reality with constitutional claims, Kaunas was designated as a temporary or provisional capital until Vilnius could be "liberated from Polish occupation". In March 1938, Lithuania accepted a Polish ultimatum, demanding diplomatic relations. Despite normalised relations, the new Lithuanian Constitution, in May 1938, still claimed Vilnius as the de jure capital of Lithuania, and Kaunas remained as the temporary capital.