Arbitration is a private system of justice that serves as an alternative to litigation. Though arbitration began as a tool for resolving disputes between businesses, recently, arbitration is frequently used in disputes between businesses and consumers in the United States. Often, arbitration agreements are commonly included in a consumer contract of adhesion, and they prohibit consumers and employees filing class actions in courts or arbitration forums. However, since individual consumers cannot carry out their private lawsuits, without class action, because their individual damage awards are too small. Though, The Federal Arbitration Act(FAA) mandates that arbitration agreements “shall be valid, irrevocable, and enforceable,” with some exceptions, such as “grounds as exist at law or in equity for the revocation of any contract.” In the United States, where class action prohibitions have the effect of allowing small but widespread illegality claims to go unheard, federal and state courts were split on whether these provisions are unconscionable. Recently, The United States Federal Supreme Court held that the FAA preempted the California’s Discover Bank rule to hold arbitral class action waivers unconscionable. However, since this decision prohibits courts from applying the unconscionability doctrine to arbitration clauses, it seriously limits the availability of consumer class actions. Therefore, this paper introduced and analyzed the United States Federal Supreme Court’s Concepcion case, regarding the enforceability of a class action waiver in a consumer adhesion of contract.