Epistolary Styles of Pseudo-Libanios (PL), a late antique manual on epistolary art, were well known to the Byzantines. The task of this article is to show that PL and its later versions were used in Byzantium as school textbooks, and to characterize their function and place in the curriculum of ἐγκύκλιος παιδεία. The research is concentrated on the Late Byzantine period (13th–15th cc.). The following texts are analyzed: PL in the original version (PL1); Epistolarium Vaticanum, an anonymous version, known in two manuscripts of the 15th c. (EV); Characteres epistolici XL, a collection of forty model letters, widespread during the Late Byzantine and Ottoman period (Ch40). PL1 was used probably within the grammar course or as a transitional link to the course of rhetoric. This is evidenced by its manuscript tradition. EV was used at the early stage of ἐγκύκλιος παιδεία, making part of the grammar course. This is clear from its content — model letters are overtly didactic in nature. The use of EV in school is also evidenced by glosses in the manuscripts. Ch40 was studied at a later stage of the educational process — as a part of the course of rhetoric. Scholia in manuscripts show that the text was analyzed with regard to the methods of rhetorical argumentation. The terminology of scholia originates in the treatise On invention, possibly written by Hermogenes of Tarsus.