The closure of St George's Benedictine convent in Prague Castle in 1782 meant the end of a valuable convent library, whose size and contents we can only conjecture. Hitherto we have been aware of a set of 65 codices to be found for the most part in the Czech National Library fonds with individual items owned by the Prague National Museum Library and the Osterreichische Nationalbibliothek in Vienna. The aim of this paper is to draw attention to the practically unknown St George codices which the Czech National Library purchased together with the Prague Lobkowicz library. These are four breviaries which were acquired by the Lobkowicz Library in 1835. Summer breviary XXIII D 156 was created before the mid-13th century undoubtedly in the environment of St George's Convent, while the somewhat older Calendarium is evidently not from St George's or of Bohemian origin at all. The winter breviary XXIII D 155 is ascribed to St George's Abbess Anezka (1355-1358). Summer breviary XXIII D 142 was created in 1359 for Sister Alzbeta, the codex decoration is from the workshop of master breviarist Grandmaster Lev. Summer breviary XXIII D 138, which is of artistic and iconographic interest, is the work of four scribes and two previously unknown illuminators.