In the article we look at the linguistic mechanism of mixing tonalities of different styles as a lexico-stylistic technique creating comic effect in Le Roman de la Rose, ou Guillaume de Dôle by Jean Renart. Lingustic mechanism for creation of comic effect in old french literary texts is based on violation of style homogeneity or, in other words, incogruity of the semantics of themes, formulas and terms and the context in which they are used. A novel, which is one of the major genres in medieval literature, is characterised by interlacement of courtly-lyrical and epic-feudal motifs. But the introduction of terms and formulas belonging to a different style (military-feudal or religious) leads to stylistic polyphony thus provoking a comic effect. Such polyphony is characteristic of Jean Renart’s style.