In this article, the authors want to study the effects of invalidity of contract on grasped property in Imamiyeh Jurisprudence and Iran's law and compare it with Egypt's law. They also indicated the viewpoints of some Imamiyeh jurists and Iranian juristic. Imamiyeh jurists account invalidity of contract to inability of ownership transfer, inviolability of possession and necessity of immediately reclamation of property and compensation. In article 308, 311 and 336 of civil code this issue has been analyzed. Iranian legislator also assume the responsibility of giver as the responsibility of usurper, if the transactions go wrong and become invalid. In the civil law of Egypt, based on article 142, the giver should modify the property if the transaction become invalid.