Udawalawe is flanked to the north by the foothills of the hill country and to the west by the foothills of the Sabaragamuwa Mountains. These highlands, dominated in the west by the peak known as Ulgala (373 metres) create a rain shadow that deprives the lowlands of the park of rain. Fortunately, however, the vegetation receives moisture all the year round from the numerous streams that flow from these hills and pass through the park.
Along the banks of the Walawe Ganga can be found thick forest. However, the rest of the area is mainly scattered grasslands and scrub jungle, which makes elephant watching easy. A stout fence encircles the park, not only to prevent the elephants from getting out, but also to stop cattle and humans getting in.
As with Yala and Wilpattu, visitors can only tour Udawalawe in 4-wheel drive vehicles.
Notable tree species include satinwood (Chloroxylon swietenia), halmilla or Trincomalee wood (Berrya cordifolia) – which was once exported in quantity to India for boat-making – ebony (Diospyros ebenum), ehala or Indian laburnum (Cassia fistula), kolon (Adina cordifolia), milla (Vitex pinnata) – which has been introduced to North America and Europe – and kon or Ceylon oak (Schleichera oleosa). However, in the riverine forest of the park it is kumbuk (Terminalia arjuna) that dominates, while in the scrubland, damaniya (Grewia tiliaefolia) is the main species.
Apart from the 500 elephants that live in the park, other mammals that can be seen include the Sri Lanka sambhur (Cervus unicolour), Sri Lanka spotted deer (Axis axis ceylonensis), Indian wild boar (Sus scrofa cristatus), toque monkey (Macaca sinica), Sri Lanka jackal (Canis aureus), Sri Lanka sloth bear (Melursus ursinus inornatus), Sri Lanka leopard (Pathera pardus fusca), Sri Lanka small civet-cat (Viverricula indica mayori), the common Indian palm-cat (Paradoxorus hermaphroditus), and the golden palm-cat (Paradoxurus zeylonensis). Of these, bear and leopard are seen only occasionally.
Notable endemics include the Sri Lanka spurfowl (Galloperdix bicalcarata), Sri Lanka junglefowl (Gallus lafayetti), Sri Lanka grey hornbill (Ocyceros gingalensis) and brown capped babbler (Pellorneum fuscocapillum). The park has many raptor species, among them the white-bellied fish-eagle (Haliaertus leucogaster), crested serpent-eagle (Spilornis cheela) and changeable hawk-eagle (Spizaetus cirrhatus).