This article is dedicated to “Diálogo de la lengua” (1535) by a Spanish grammarian of the Renaissance Juan de Valdés whose personality and works are not so widely known in Russia. “Diálogo de la lengua” represents the Renaissance dialogue, heir to the Greek-Latin traditions and is dedicated to the Castilian language, the interrelation of its norms and Language Usage, stylistic and lexical issues. The attention is focused on the genre features of “Diálogo” and the relationship of the author and the character to represent him in the dialogue. The analysis is conducted in terms of a combination of various stylistic and genres features of the language in the “Diálogo” making it possible to distinguish the traits of scientific style in the work (and to consider the “Diálogo de la lengua” as a grammar of the Castilian language and linguistic comment), as well as a work of art (scenic or philosophical Socratic dialogue).