This article aims to describe the application of the standard of proof in arbitration and to question whether the standard to be applied should be the same as or lower than in ordinary civil justice as a result of the contractual origin of the dispute. The determination of the applicable standard takes into consideration the equality of arms and other guarantees of due process, along with the fact of the absence of the standard rule in the Arbitration Act 1996. The arbitrator shall establish these aspects at the beginning of the process, considering also the rules of burden of proof.