Meganthropus is an extinct genus of pongine hominid ape, known from the Pleistocene of Indonesia. It is known from a series of large jaw and skull fragments found at the Sangiran site near Surakarta in Central Java, Indonesia, alongside several isolated teeth. The genus has a long and convoluted taxonomic history. The original fossils were ascribed to a new species, Meganthropus palaeojavanicus, and for a long time was considered invalid, with the genus name being used as an informal name for the fossils.

In the mid-2000s the taxonomy and phylogeny for the specimens were uncertain, and most paleoanthropologists considered them related to Homo erectus in some way. However, the names Homo palaeojavanicus and even Australopithecus palaeojavanicus were used as well, indicating the classification uncertainty.

After the discovery of a robust skull in Swartkrans in 1948 (SK48), the name Meganthropus africanus was briefly applied. However, that specimen is now formally known as Paranthropus robustus and the earlier name is a junior synonym. Some of these finds were accompanied by evidence of tool use similar to that of Homo erectus; this is why Meganthropus was often linked with that species as H. e. palaeojavanicus. In 2019, a study of tooth morphology found Meganthropus a valid genus of non-hominin hominid ape, most closely related to Lufengpithecus.

The number of fossil finds has been relatively small, and it is a distinct possibility that they are a paraphyletic assemblage. Due to this, they will be discussed in detail separately.

This large jaw fragment was first found in 1941 by Gustav von Koenigswald. Koenigswald was captured by the Japanese in World War II, but managed to send a cast of the jaw to Franz Weidenreich. Weidenreich described and named the specimen in 1945, and was struck by its size, as it was the largest hominid jaw then known. The jaw was roughly the same height as a gorilla's, but had a different form. Whereas in anthropoids the mandible has its greatest height at the symphysis, that is, where the two rami of the lower jaw meet, this is not the case in Sangiran 6, where the greatest height is seen at about the position of the first molar (M1).

Weidenreich considered acromegalic gigantism, but ruled it out for not having typical features such as an exaggerated chin and small teeth compared to the jaw's size. Weidenreich never made a direct size estimate of the hominid it came from, but said it was 2/3 the size of Gigantopithecus, which was twice as large as a gorilla, which would make it somewhere around 8 feet (2.44 m) tall and approximately 400 to 600 lbs (181 – 272 kg) if scaled on the same proportions as a robust man or erect hominid. In his book Apes, Giants, and Man, Weidenreich states the following:

Therefore, it may not be too far from the truth if we suggest the Java giant [Meganthropus] was much bigger than any living gorilla and that the Chinese giant [Gigantopithecus] was correspondingly bigger than the Java giant – that is, one-and-a-half times as large as the Java giant, and twice as large as a male gorilla.

The jawbone was apparently used in part of Grover Krantz's skull reconstruction, which was only 21 cm (8.3 in) tall.