The parties to arbitration can agree on the applicable law, however, in case of lack of determination, the arbitrator shall determine it according to the appropriate conflict of law rules. Also, the arbitrator can interpret and determine the applicable law. If the applicable law is disregarded, since the arbitral award is final and the act determines the grounds to challenge, the parties cannot challenge the award. Iran’ s International Commercial Arbitration Act does not determine disregarding applicable law as a ground for challenging the award, so the parties’ autonomy and finality are in contrast. The research shows that although the court cannot review the award beyond the expressed grounds, parties can add some grounds to it. In some cases, the disregard of the applicable law could be interpreted as to act out of mandate or or lack of impartiality.