Udawalawe (; also spelled Udawalawa) is a town in the southern part of the Ratnapura District in Sabaragamuwa Province, Sri Lanka. It lies near the district boundary with the Hambantota District and Monaragala District, approximately southeast of Colombo.
The town is situated in the dry zone of southern Sri Lanka, in the lowland plains south of the central highlands. The Walawe River, one of the major rivers in southern Sri Lanka, flows through the area. The river's catchment above the town covers . The surrounding landscape includes scrubland, grassland, and remnant forest.
The Udawalawe Dam and Reservoir were constructed as part of the Walawe Ganga Scheme, completed in 1965. The dam, comprising both embankment and gravity sections, has a total length of approximately and crosses the Walawe River. The reservoir has a total capacity of 267 million cubic metres and a surface area of . It extends approximately in length and in width.
The reservoir's primary purpose is irrigation, supplying water to agricultural land in the surrounding region. The Walawe Ganga Scheme also involved the construction of Chandrika Wewa () and Ridiyagama Reservoir ().
The Udawalawe Power Station, operated by the Ceylon Electricity Board, was commissioned in April 1969. It has an installed capacity of 6 MW, generated by three 2 MW turbine units manufactured by CKD Blansko of Czechoslovakia. The station produces an estimated 8 GWh annually. Water levels in the reservoir are regulated by five tainter gate spillways at the eastern end of the dam and two additional spillways near the centre.
The town is the main entry point to Udawalawe National Park, established on 30 June 1972 to provide a sanctuary for wildlife displaced by the reservoir's construction and to protect the reservoir's catchment. The park covers and is the third most visited national park in Sri Lanka. It is known for its large population of Sri Lankan elephants.