Dositheus the Grammarian was a Greek grammarian active in the 4th century CE. His career belongs to the late antique period, when grammatical education remained central to Greco-Roman paideia. The 10th-century Byzantine encyclopedia, the Suda, mentions a grammarian of this name who authored a work on the eight parts of speech, though this attribution is not certain.

His sole definitive work is a bilingual Ars Grammatica, a grammatical manual presented in parallel Greek and Latin columns. It systematically covers the parts of speech, morphology, and syntax, functioning as a school text for language learners in the bilingual context of the later Roman Empire.

Dositheus’s manual is a crucial artifact of late antique education. It provides direct comparative evidence for contemporary Greek and Latin grammatical structures and terminology. Its format makes it a key source for understanding pedagogical methods, linguistic contact, and the history of grammar in the 4th-century Roman world.