This article re-examines the identity and chronology of the lexicographer Boethus, by analyzing three pieces of evidence. It is argued that the lexicographer Boethus is a Middle Platonist flourishing in the late first or early second century, who believed in the transmigration of souls and was engaged in exegesis of Plato. In particular, this article draws attention to a testimony on Boethus from a newly discovered treatise preserved in Syriac, which is identified as Porphyry’s On Principles and Matter.