Phthiotis (Gr. Phthiotis 1300465 ), the southernmost district of ancient Thessaly. It extended from Dolopia and the S. E. portion of the Pindus range on the west to the Pagasiean gulf on the east, and from the Narthacian mountains, near Pharsalus, on the north, to the Maliac gulf on the south. The Othrys range passed through its central part. It derived its name from the Phthia of the Homeric poems, a country of much larger extent apparently than the subsequent district, for it is represented as including Hellas and Dolopia as well as the region about Pharsalus. Phthiotis was inhabited by Achasans. The chief towns of the district were Thebes (Thebaa Pthiotides), Halus, Pteleum, Antron, Larissa, Lamia, Xynise (near Xynias lake), Thaumaci, and Itonus. - The modern Greek nomarchy of Phthiotis and Phocis, having Phthiotis for its northernmost eparchy, includes only the southern portion of the ancient district, its northern boundary extending along the Othrys range.

The area of the nomarchy is 2,053 sq. m.; pop. in 1870, 108,421. Capital, Lamia or Zeitun.