Fairness in law is the full and complete granting the right for every rightful and lacking any shortcoming and weakness in granting of individual rights. In Islam, however, the importance of justice in law has been emphasized and the purpose of sending divine prophets has been introduced as performing of justice. In other words, the justice is the spirit of Islamic law. So our question in this article is, can the principle of fairness be invoked in the performance warranties for breach of contract? Our hypothesis, which can be concluded as the general conclusion of this article, is that the acceptance of the rule of justice as a documentary and source of judgment in the performance warranties for breach of contract, although it is accepted in some international law and arbitrations, but in Iranian law, the rule of justice cannot be cited as a source of judgment, although this rule can be applied to the interpretation and application of the provisions of the law to the circumstances of the litigation.