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The contract is result of agreement. Sometimes, after the conclusion of a contract, one of the parties understands that in the time of conclusion it hasn’t been equilibrium between the subjects of contract that there is "option of loss". Sometime in the time of conclusion, there is economic equilibrium but during of executing of contract this balance disappears and execution of contract is so difficult that customarily is not tolerable. In the other words, there is a “new loss”. In Iranian civil law, when there is loss in the time of conclusion, there is option of loss by principle of “no harm” and other sources. But after the conclusion of contract, when the balance grossly disappears, there is no solution. In the law of some of Islamic countries the judge can reasonably adjust the parties' obligations. It shows that the basis of adjustment can be fined in the Islamic law and the examination of Islamic texts shows that the adjustment has been regarded profoundly. This article wants to bring up the subject of adjustment with use of Islamic reasons and comparative law