One of the important and influential issues in international commercial arbitration is the identification and application of mandatory rules, which are subject to the will of the states and any agreement contrary to it is null and void. Accordingly, when the stage of identification and enforcement of the award arrives, the first obstacle that emerges is the mandatory rule. Based on the descriptive-analytical method, the present study seeks to answer the question: When is mandatory rules enforced in international commercial arbitration? And what is the effect of not applying mandatory rules in international commercial arbitration? The hypothesis and findings confirm that courts are required to comply with mandatory rules when enforcing the award, and arbitrators must consider the mandatory rules of all countries involved in the arbitration during the proceedings and strive to comply with and apply them. Otherwise, failure to apply mandatory rules and their violation in the arbitration proceedings can lead to the invalidity or non-enforcement of the arbitral award.