Nimule National Park is located in the extreme south of the country on the border with Uganda. It was established in 1954, and extends over an area of 410 kilometers. Nimule National Park is characterized by deciduous tree species typical of the savannah and bush environments as Kigelia africana, Acacia seyal, A. abysinica, A. sieberiana and A. brevispice, Schelerocharya birrea, Afteli aquanzensi, Ziziphus mouritiana, Euphorbia candelabrum, Combretum molle, Tamarindus indica, Borasus aethiopium, Anona senagalensis, and Caesesalpinia decapetala. Riverine woodland vegetation is present, occurring along seasonal and permanent rivers and streams. The Kayu River that flows through the park from the Uganda border to the hills and the Illunga mountains are some of physical features of Nimule National Park.

The White Nile forms the eastern border of the park for 48 kilometers. On the eastern bank, there is a buffer zone, bounded by the Assua River to the north and by the Juba - Nimule road to the east. The Kayu River flows through the park from the Uganda border to the White Nile. The topography is hilly and most of the park is covered with savanna woodland of Acacia, Balanites aegyptiaca and Combretum aculeatum. Riverine woodland, found along permanent and seasonal watercourses, is composed principally of Acacia sieberiana and Borassus aethiopium. The site is contiguous with two Important Bird Areas in Uganda; Mount Kei Forest Reserve and Mount Otzi Forest Reserve.

Biodiversity in Nimule National Park and the surrounding buffer suffered intensive threats e.g. poaching, human encroachment, cattle keeping, deforestation and other anthropogenic activities that were carried out by people living nearby during the South Sudan 2013 - 2019 civil war. These threats are currently actively controlled by the park rangers with a priority toward illegal hunting and bushmeat trading. A total of 1207 bird spieces are recorded in the park.