In the first half of the 13th Century, Aristotelianism was newly introduced into the West from the Moslem and Jewish world. But on the other hand, the traditional thought of the West, namely Augustinianism still remained influential. Therefore, there is a very interesting problem about the inter-relation between the traditional Augustinianism and the newly introduced Aristotelianism. In this thesis I examined what attitude St. Bonaventure, one of the representative Augustinians of the 13th Century, showed toward Aristotelian philosophy. Mr. Gilson insisted that St. Bonaventure could not admit purely rational and natural philosophy in his system of thought. In Mr. Gilson's opinion, St. Bonaventure was convinced of the weakness of human reason left to its own lights without the help of revelation. Therefore, a close collaboration between reason and faith was necessary to attain the certain knowledge, not only of supernatural things, but also of natural things. Thus, in Mr. Gilson's opinion, the philosophy of St. Bonaventure was Christo-centric and was heterogenous to all natural or, pagan philosophies such as. Aristotle's; Furthermore, Mr, Gilson says, St. Bonaventure had absolutely been to Aristotelian philosophy from his younger days. But in the Commentary on the Sentences, the main work of his younger days, St. Bonaventure shows neither hostility nor enmity to Aristotle. On the contrary, he appreciates almost all the basic principles of Aristotle. He even calls Aristotle "ille excellentior inter philosophos". Therefore it may be argued that Mr. Gilson's opinion includes something of exaggeration. But I also can not agree with Mr. Van Steenberghen's opinion that the philosophy of St. Bonaventure was an eclectic neo-platpnicising Aristotelianism employed in the service of Augustinian theology. It is time that we can find many elements of Aristotelian philosophy in St. Bonaventure's works. But inspiration of his philosophy is totally different from that of St. Thomas or any other Aristotelian philosophers. It is true that in St. Bonaventure's opinion, natural reason can attain relative and transient certainty of knowledge. But he severely denies that it can attain absolute and eternal certainty without divine illumination of rationes aeternae. In this basic standpoint, St. Bonaventure's philosophy has very clear Augustinian tendency.