The arbitration agreement should be considered as a collateral contract which is inserted in the main on tract (sale, carriage of goods, insurance, etc).Therefore, the question raised is whether the invalidity of the main contract could have any legal effect on the arbitration agreement. In case the response would be positive, we should admit that we are, here, facing a vicious circle, for, the arbitrator who makes a decision declaring the main contract invalid, declares in fact that he has no competence to decide as an arbitrator due to the fact that the invalidity of the main contract means that the arbitration clause was invalid as well.For the purposes of preventing such a dilemma most legal systems have opted for the theory of severability of the arbitration agreement and, therefore, do not consider that in case of the invalidity of the main contract the arbitration agreement should be considered invalid as well.The theory of severability has been admitted by the Iranian Law on International Commercial Arbitration, but rejected by the Code of Civil Procedure.The object of this article is to study the issue in question in comparative law as well as to analyze and evaluate the so called dualistic solution adopted by the Iranian legislation.