The name and subject of this article is changing the content of rental agreements on immovable properties by implicit declaration of intent. This study was prepared by comparing the related provisions of Turkish Code of Obligations, Law Nr. 6098, Law of Obligations, Law Nr. 818 and the Law on Rental Agreements on Immovable Properties, Law Nr. 6570. In this context, first of all, the concept of implicit declaration of intent was explained. Next, the content of contracts in general, and specifically the content of rental agreements was explained. Then, groups of events which can be deemed changing the content of rental agreements by implicit declaration of intent and later those which can not be were explained. The subject matter of this study was handled in the light of Turkish Code of Obligations, Law Nr. 6098 (The New Code), Law of Obligations, Law Nr. 818 (The Ex-code) and the Law on Rental Agreements on Immovable Properties, Law Nr. 6570 (which will cease to have effect).