Philoxenus of Cythera (Greek: Φιλόξενος ὁ Κυθήριος; c. 435/4 – 380/79 BC) was a Greek dithyrambic poet, an exponent of the "New Music". He was one of the most important dithyrambic poets of ancient Greece.

Few details of Philoxenus' life are known. According to the Suda, Philoxenus was the son of Eulytides, from Cythera. On the conquest of the island by the Athenians, Philoxenus was taken as a slave to Athens, where he came into the possession of the dithyrambic poet Melanippides, who educated him.

Philoxenus lived for some time in Sicily, as the court-poet of Dionysius, tyrant of Syracuse. There, according to Athenaeus—probably based on an account by the 4th-century philosopher Phaenias of Eresus—Philoxenus tried to seduce Dionysius’ mistress Galateia, and was thrown into the quarries. However, according to Diodorus Siculus, Philoxenus' imprisonment in the quarries was the result of his refusal to praise Dionysius' bad poetry:

In Sicily Dionysius, the tyrant of the Syracusans, now that he was relieved of wars with the Carthaginians, enjoyed great peace and leisure. Consequently he devoted himself with much seriousness to the writing of poetry, and summoning men of repute in this line, he accorded them special honours and resorted to them, making use of them as instructors and revisers of his poems. Elated by the flattering words with which these men repaid his benefactions, Dionysius boasted far more of his poems than of his successes in war. Among the poets in his company was Philoxenus, the writer of dithyrambs, who enjoyed very high repute as a composer in his own line. After dinner, when the compositions of the tyrant, which were wretched, had been read, he was asked what was his judgement of the poetry. When he replied with a good deal of frankness, the tyrant, offended at his words, found fault with him that he had been moved by jealousy to use scurrilous language and commanded his servants to drag him off forthwith to the quarries. On the next day, however, when Philoxenus' friends made petition for a grant of pardon, Dionysius made up with him and again included the same men in his company after dinner. As the drinking advanced, again Dionysius boasted of the poetry he had written, recited some lines which he considered to be happily composed, and then asked, "What do you think of the verses?" To this Philoxenus said not a word, but called Dionysius' servants and ordered them to take him back to the quarries.

After leaving Sicily, according to the Suda, he lived for a while in the Greek colony of Taras (modern Taranto) in Italy, and died at Ephesus. According to the Parian Chronicle, he died in 380/79 BC, at the age of 55.

The great popularity of Philoxenus is attested by a complimentary resolution passed by the Athenian Senate in 393 BC. A character in a comedy by Antiphanes spoke of him as "a god among men"; Alexander the Great had his poems sent to him in Asia; the Alexandrian grammarians received him into the canon; and down to the time of Polybius his works were regularly learned and annually performed by the young men of Arcadia.

Philoxenus was a poet-musician, one of the most important of his era. He was a so-called "New Music" poet, representing a style that developed between the end of the 5th century BC and the first decades of the 4th century BC. He, along with other such "New Music" poets as Melanippides and Timotheus, introduced significant changes in music. These included adding to the number of strings on the cithara, introducing complex melodies with more notes and larger intervals between notes, and using multiple changes of harmonies and rhythms in a single work.

Philoxenus introduced other innovations, for example while the traditional dithyramb was a choral song accompanied by the aulos, Philoxenus' Cyclops sang a solo accompanied by the cithara. And, in another innovation for dithyrambic performance, the same character was apparently supplied with a costume, which included a leather bag, and sprigs of herbs.