(Σωσίθεος), of Syracuse or Athens, or rather, according to Suidas, of Alexandreia in the Troad, was a distinguished tragic poet, one of the Tragic Pleiad, and the antagonist of the tragic poet Homer : he flourished about Ol. 124 (B. C. 284); and wrote both in poetry and in prose. (Suid. s. v. He is also mentioned among the poets of the Pleiad in all the lists except that of Tzetzes.

The remains of his works consist of two lines from his (Stob. Serm. 51.23), and a considerable fragment of twenty-four lines from his or Λιτυέρσας, which appears to have been a drama pastoral in its scene, and in its form and character very similar to the old satyric dramas of the Attic tragedians. (Schol. apud Casaub. ad Theocr. 100.12; comp. Ath. x. p. 415b; Tzetz. Chil. 2.595; Schol. ad Theocr. 10.41.) By some of the above authorities the name Sosibius is wrongly given instead of Sositheus. Another error, into which some writers have been led by the character of the Δάφνις of Sositheus, is that of making him a comic poet. (Fabric. Bibl. Graec. vol. ii. pp. 322, 323, comp. p. 495; Clinton, F. H. vol. iii. s. aa. 278, 259, pp. 501, 502; Welcker, Griech. Trag. p. 1052; Wagner, Frag. Trag. Graec. in Didot's Bibliotheca, pp. 149-152.)