Once the defendant’s breach of contract has been established, it is often said that the claimant comes under a duty to mitigate his loss. The consequence of the failure to mitigate is that the part of the loss suffered by the claimant which is attributable to the unreasonable action or inaction of the claimant becomes irrecoverable. The so called duty to mitigate loss comprises two separate functions. First, the claimant must not take any step which unreasonably increases the loss suffered in consequence of the defendant’s breach of contract. This rule only applies to expenses incurred after breach. Other unreasonable acts will be treated as an intervening cause of the harm suffered. Secondly, the claimant must take such reasonable and positive steps as are necessary to minimize the loss he or she suffers. For example, a wrongfully dismissed employee must attempt to find a comparable job, and where a seller fails to deliver goods, the buyer must go into the market to obtain substitute goods. This rule is a rule of common law but it seems that this rule is accepted in Imamieh-feqh. Also its effects may be accepted in Iranian law. This rule is a rule of common law but it seem that this rule is accepted in Imamieh-feqh. Also its effects may be accepted in Iranian law.