In the residential and commercial premises lease agreement, the parties may choose to conclude a new lease agreement by determining a new rental price after signing the lease agreement. Some problems may arise with the new contract signed. Some of these problems can be stated as; whether the rent determined in the new lease agreement is valid or not, which periods should be taken into consideration in determining the rent based on the precedent after the new agreement, and the legal status of the guarantees. In the first part of the study, the validity of the new rental price determined by the parties will be discussed. In the second part, the legal nature of the new agreement will be discussed. In this context, discussions such as whether the parties have made adaptation, whether the second agreement is a modification agreement that envisages changes in the first signed agreement, or whether it is an independent novation agreement that is completely different from the first agreement will be discussed. After these discussions, the legal consequences depending on the legal nature of the contract will be discussed.