Taxpayers' declaration of their income in tax systems is important in terms of ensuring the participation of taxpayers in taxation process. However, it is not always possible for taxpayers to carry out their taxation completely and accurately. In order to eliminate these deficiencies in the taxation process, Turkish Tax System has repentance and correctional institution. The legislator has included the application of mental reservation in the tax return system in order to prevent the loss of rights in relevant of the situations which taxpayers are hesitant. Mental reservation, is a legal opportunity that serves the taxpayer the right to file a lawsuit against his/her own statement by writing a note in it. Repentance and correctional institution is the one of the cases that prevent tax penalty and also is one of the solutionary ways of tax disputes in the administrative phase. The subject of this work is the question of whether the declaration given in the attachment of the petition of repentance can be submitted with mental reservation or not. In this context, firstly repentance and correctional instituion, its legal nature, its scope and its conditions of utilization will be explained. And then it will be examined that the declaration given in the attachment of the petition of repentance for correction is a separate declaration or not. Right after the notion of mental reservation will be explained and the opinions in the doctrine about whether or not the declarations given in the attachment of the petition of repentance can be given with the mental reservation will be discussed with their grounds. The study, which also includes court decisions, ends with a concluding section that includes our overall evaluation.