The purpose of this study is to analyze concepts and ideas on litterae represented in the Etymologies of Isidore of Seville. Explications on various aspects of litterae, including etymologies, inventors, functions, Latin and Greek alphabets, etc., appear in the First Book of Etymologies, entitled as “De Grammmatica (On Grammar).” Isidore of Seville inherited his compilations on litterae from Latin grammarians` commentaries on Donatus in the Late Empire and in the early Middle Ages, and from the Fathers of the Church, in particular, from Saint Augustine. Nevertheless, the organization of Etymologies and the treatment of materials discloses a certain alteration, especially when it comes to the idea of litterae in the early 7th century. Isidore of Seville begins his chapter on grammar with explications on litterae, just following the definition of disciplina and ars, whereas other grammarians generally start their treatises with the chapter on voice. It signifies that Isidore considers litterae to be the foundation of knowledges and studies, and places great weights on them. He also accentuates on the visual aspect of litterae which permits visual communication with the absent without voice. I concur with the argument of M. B. Parkes that Isidore`s considerations on litterae testifies the transformation of the status perception of the written words in his time, in that they are perceived as visual vehicles of communication filled with symbolic meanings.