Private contracts are void if they contradict public order but where should the courts look for “public order”?  should courts only cite “public order’ when the order is arise from imperative acts or general legal principles? Or it can be derived from other sources like customs, social traditions, ethis and shari’a too? This paper will consider this debate in Iranian civil law and jurisprudence and in a comparative study it also have look on other legal systems, namely American, British and French legal systems. This paper concludes that the imperative Laws in a general sense (spirit and concepts behind laws and legal general policies and principles) should be considered source of “public order’ And a synthesis of imperative law and public order should be used instead of believing in independence of public order from imperative law. While ethics and sharia must be accepted as two independent controlling source for the principle of contractual freedom.