Sadi is one of the few Persian poets whose fame and eternal presence in the Persian culture rests mostly on the effect of his works. This study is an effort to investigate the relationship between his didactic, rhetorical, religious and ethical poems and the principles of the Ash'ari school of rhetorical thought. To this end, we will define the discipline of rhetoric and mention its characteristic features as well as the reasons for its emergence and development, and also the probable weaknesses and failure of the Mo'tazele and Ashare. The two dominant schools of rhetoric in the Islamic civilization will be given special treatment. However, in the final section of the project, entitled "Sa'di's school of Rhetoric" the historical background and the reasons for Sa'dis tendency toward Ash'ari school will be explained.  Finally evidence for this tendency and reflections of his Ash'ari thought samples will be extracted from his poems and will be classified and explained under the common rhetorical topics such as "divine sight", "divine justice", and "determinism and free will