The Principle of "Taadol Tarafoei" which is also referred as "Tanazaor Principle" is one of the principles of fair trial. This is as the primary principle in all judicial systems in the world. This means that there should be fair deal between parties. Hence, violating this principle causes injustice in trial. This principle which is the base of justice is indicated in international documents such as European Convention of Human Rights. However, in none of Iranian laws we donât see it as the principle for establishing justice in judicial trial. The present article tries to study the base and nature of this principle in Islamic law and international documents.