The principle of the need to provide reasons for administrative decisions is one of the new concepts of administrative law. However, the two important elements of the mentioned principle, i.e., the effectiveness of the reasons and the rationality of the reasons for the decision, have not been taken into consideration, and most of the discussions in this field have been focused on its concept and foundations. In this regard, considering the position of this principle in administrative law, addressing the dimensions and various elements mentioned can help to enrich the said principle. In addition, the study of the concept of effective and reasonable reasons reveals the distinction of their application in public law and especially in administrative law compared to civil and criminal law. In this regard, in this article, the descriptive-analytical method and the use of library tools, while explaining the concept, requirements, foundations and elements of the effectiveness and rationality of administrative decisions, the distinctions and differences of these two sharp elements have been discussed. The results of the research indicate that the two mentioned elements are different in terms of their concept and components, as well as in terms of their foundations, in such a way that effective reasons are rooted in legal rules, but reasonable reasons are based on logic data. Humanity and the standards of fairness. And finally, the conclusion has been reached that effective reasons are rooted in law and justice, while reasonable reasons have logical and fair foundations