Poloniny National Park is a national park in north eastern Slovakia at the Polish and Ukrainian borders, in the Bukovské vrchy mountain range, which belongs to the Eastern Carpathians. It was created on 1 October 1997 with a protected area of 298.05 km² and a buffer zone of 109.73 km². Selected areas of the park are included into Primeval Beech Forests of the Carpathians UNESCO World Heritage Site.
The park is located in the Snina District in the Prešov Region. It is adjacent to the Bieszczady National Park in Poland, together they are part of the East Carpathian Biosphere Reserve. The highest point lies at 1,208 m (3,963 ft) AMSL on a point where the borders of Slovakia, Poland and Ukraine meet, near the summit of the mount Kremenec. National Park is the easternmost and the least populated area of the country. Hiking trails starts from several villages, most notably Nová Sedlica but also from Runina, Topoľa and Uličské Krivé.
Forests cover about 80% of the area; beech and beech-fir forests are dominant. The National Park has the highest concentration of old growth forests in Slovakia, which are protected by national nature reserves. Meadows, called poloniny in Eastern Slovak dialects, situated on the main ridge of the Bukovské vrchy mountain range are common.
Many species found in the park are endemic and rare. Altogether, 800 fungi and 100 lichens are native to Poloniny. The Poloniny National Park contains about 5,981 known species of invertebrates (for example, 91 molluscs, 1,472 true bugs, 819 butterflies, and 403 spiders) and 294 vertebrates. Vertebrates divide into 13 amphibians, 8 reptiles, 198 birds, 55 mammals, including the Eurasian lynx, bear, and others. About 1,000 species of vascular plants have been found in the park. Many of them are endangered and protected. Small herd of wisent (Bison Bonasus) was reintroduced in the area in 2004.