Doubts and disagreements over the nature of the liability arising from delay in execution of monetary obligations have led to disagreements between the authors in accepting it. The extra contractual nature of this liability is similar to usury and interest, while its contractual nature is merely a requirement to fulfill a full obligation and does not contradict the public policy rules (such as the prohibition of usury and interest). Liability arising from delay in execution of monetary obligations is stipulated in article 522 of Iranian civil procedure Law and article 1231-6 of French civil Law (2016). Although both regulations express that, in cases of debtor delay to execution of monetary obligation, he is required to pay an additional amount of the original debt to creditor, but nature of liability arising from delay in execution of monetary obligations is different in Iranian and French law. Nature of this liability is matter of dispute in Iranian law, and correct opinion is that nature of liability arising from delay in execution of monetary obligations is contractual and the purpose of creating this responsibility by the legislature is to compensate for the devaluation of the money and obliges the debtor, in addition to the amount of the subject of the obligation, to compensate for its devaluation, in order to completely fulfill his obligation but in French Law, nature of this liability is extra contractual and the debtor which has delayed to execution of monetary obligation, irrespective of whether the value of the money has been reduced, is obliged to pay the excess amount of the original debt as a damages according to the legal rate. In addition to changing the annual price index, in Iranian Law, there are requirements for demand compensation of delay in execution of monetary obligations, Such as creditorchr('39')s demand and debtorchr('39')s possibility, on the other hand, in French law debtorchr('39')s possibility is not necessary. In future amendments, the legislature should consider the contractual nature of this liability in Iranian law and determine the conditions accordingly.