There is a need to determine law applicable for several issues in international commercial arbitration. One of such an issue, in case when arbitration agreement is concluded by plenipotentiary, is to determine law applicable for power of attorney to conclude an arbitration agreement and its form. Paper presents the nature of the power of attorney to conclude arbitration agreement and conflict of laws rules, intended to designate law applicable for plenipotentiary to conclude arbitration agreement, which are in force in Republic of Poland. These rules include the choice of law, as well as the cascade conflict of laws rule based on objective connecting factors. Article contains considerations on the law applicable to the form of power of attorney to conclude an arbitration agreement. The study presents the relationship between issues governed by law applicable for power of attorney and issues governed by law applicable for arbitration agreement.