The Javan rhinoceros, Javan rhino, Sunda rhinoceros or lesser one-horned rhinoceros is a critically endangered member of the genus Rhinoceros, of the rhinoceros family, Rhinocerotidae, and one of the five remaining extant rhinoceros species across South Asia and Africa. The Javan rhinoceros is one of the smallest rhinoceros species, along with the Sumatran, or "hairy", rhinoceros. They are superficially similar to Indian rhinos, as they have plate-like, "armored" protective skin folds, but are slightly smaller in size, at just 3.1–3.2 m (10–10 ft) long and 1.4–1.7 m (4.6–5.6 ft) tall, on average. The heaviest specimens weigh around 2,300 kg/2.3 tonnes, similar to a black rhinoceros. However, unlike the long and potentially lethal horns of the black or white rhinoceroses of Africa, the Javan species' single, somewhat blunted horn is usually shorter than 25 cm (9.8 in).

Rhinoceros is a genus comprising one-horned rhinoceroses. This scientific name was proposed by Swedish taxonomist Carl Linnaeus in 1758. The genus contains two species, the Indian rhinoceros and the Javan rhinoceros. Although both members are threatened, the Javan rhinoceros is one of the most endangered large mammals in the world with only 60 individuals surviving in Java (Indonesia). The word 'rhinoceros' is of Greek origin meaning "nose-horn".