Arbitration, the most preferred dispute resolution approach, achieves its effectiveness through the well-known principles. Parties’ duty to act with procedural good faith is summarized in parties’ coop- eration to submit the relevant documents, clean hands theory, and pro- hibition of inconsistent behavior. There is no standard test to consider how parties have observed the principle, and cases show instances, in- cluding any attempt to mislead the court through the fabricated evi- dence, demonstrating the breach of the principle of good faith. The pro- cedural good faith aims to administer the best and proper conduction of Arbitration. This paper compares the party’s duty to act with good faith in Iran and the English legal system by analytical and description methods.