塞伊内（Sejny）是位于波兰东北部的城市。在1999年，有人口约6,500人。是一座旅游城市。在中世纪就有人居住。二战期间，这里的犹太社区都被驱逐。

Sejny [ˈsɛi̯nɨ] (Lithuanian:Seinai) is a town in north-eastern Poland and the capital of Sejny County, in Podlaskie Voivodeship, close to the northern border with Lithuania and Belarus. It is located in the eastern part of the Suwałki Lake Area (Polish:Pojezierze Suwalskie), on the Marycha river (Seina in Lithuanian for which the town was named), being a tributary of the Czarna Hańcza. As of 1999 it had almost 6,500 permanent inhabitants, with a strong seasonal increase during the tourist season.