One of the most important concepts and indicators in the Islamic Economic System is fairness. The present study intends to examine this important rule in the economics literature and Islamic texts in order to analyze its various dimensions and aspects. In the present study, the functions of fairness are described in four field in the legal system of economy, international trade, transactions and banking. The added value of the present research is that fairness is one of the policy instruments for evaluating and monitoring the Economic System performance. Finally, some teachings of this important rule are presented to improve domestic and international Economic Systems. Institutionalizing and realizing fairness in the Economic System leads to the justice of the information system, reduce the control cost, realize the fair system of information flow in order to secure the right, fairness in determining the production profit or the added value of commodity, resolve the problem of transparency and symmetry of information in financial markets, the social balance in economic issues, improve the accountability in Economic System.