SUMMARY: In this paper the author gives a synthetical exposition of Roger Bacon's do-ctrine on human wisdom as it appears in his chief work — the «Opus Maius», sent to Pope Clement IV in defence of his teaching. The work is subdivided info seven parts: (a) elimination of the four causes of human error — the tendency of hiding one's own ignorance under the veil of false wisdom, submission to unworthy authority, influence of wrong scientific ha-bits, acriticai acceptance of popular prejudice; (b) Holy Scripture as the source of ali wisdom; (e) knowledge of languages with special emphasis on the practical importance of a scientific study of languages; (d) mathematics and its various applications; (e) optics, neces-sary to explain physical phenomena and the complex structure of the universe; (f) experi-mental science as an autonomous discipline characterised by its influence on ali the other sciences; (g) moral philosophy, instructing man in his relationship with God, his fellow men nd himself. Like Bonaventure, Bacon is not satisfied with the acquisition of the «sermo ientiae» as taught by Aristotle and based on abstractive cognition, but, always faithful to e platonic-augustinian spirit of the franciscan tradition, he would rather enrich himself by e «sermo sapientiae» through divine illumination. The paper ends with a modest evalua-on on the personality of the franciscan thinker under the philosophical aspect.