According to the article 190(4) of Iranian Civil Code, one of the fundamental conditions for the validity of a contract is legitimacy of the motive of the contract. According to article 217 of Civil Code, the transaction with illegal motive is null. But, if illegitimacy of the motive is included in the contract expressly, and if it is immediate and clear, it will result to invalidity of the contract. The validity of the transaction with illegitimate motive and without clear knowledge of it and without it's insertion in the transaction is subject to debate. In Islamic jurisprudence, dealing with illegitimate motive is forbidden (Haram) by reasons such the wisdom ruling to ugliness of helping sin, the verse “do not help each other in sin and transgression” and the necessity of forbidding evil. Although the bargain with illegitimate motive is illegal by the consensus of scholars, but there is disagreement on its nullity. According to some jurists it is null and void and according to the others, it is valid. The present article by invoking to article 217 of Civil Code and the rule of the authenticity of the transactions accepts the latter view.