The principle of the sovereignty of will, when accompanied by traditions such as "Al-Momenoon al-Ihrrvmvm", is the result of the verity of any condition which is entered into the contract, except in circumstances which have been proven by the external reason, the void or the incorrectness of them. One of the conditions that is doubtful is the mortgage condition while making surety. In this way, the deposit of a surety in favor of the guarantor or the content of the loan will be mortgage. The mortgage condition in the contract of guarantee is considered as the subject of jurisprudence and it seems that the first jurisprudent who has mentioned this issue is Seyed Yazdi. Since the design of this issue, the jurists have disputed the validity of this condition. The present paper uses a descriptive-analytical method based on the library method. This study seeks to verify the validity of this condition. In my opinion, the benefit of the mortgage condition, whether it is in favor of the guarantor, should be regarded as a valid condition.
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