A new synthesis pathway toward hydrogen peroxide has been investigated using non-thermal plasma. This work is aimed at studying the activation of oxygen/hydrogen mixtures by a cylindrical dielectric barrier discharge. An experimental device has been especially developed for this application, it mainly differs from other cylindrical discharges in that the liquid ground electrode, and subsequently the reactor, can be regulated in temperature. The formation of hydrogen peroxide is reported (1) in a gas phase discharge and (2) in surface discharge. The gas phase discharge, characterized by an empty discharge gap, lead to a low activation of O-2 into O-2/H-2 mixtures and poor selectivity toward H2O2. The modification of the discharge into a surface discharge, by introducing in the gap fibrous materials, considerably improves the efficiency of the process. The influence of the temperature on H2O2 formation is discussed and correlated to the formation of a water layer on fibre surface. This layer appears to be a crucial point into H2O2 plasma synthesis. The presence of TiO2 on the fibre surface is reported as improving the stabilisation of hydrogen peroxide. The formation of a complex between H2O2 and TiO2 is suggested and discussed. The formation of H2O2 in the gas phase or in the aqueous condensed phase is finally discussed. The investigation of the influence of the reactant gas composition and the presence or not of water, lead to the conclusion that (1) both H-2 and O-2 are required to achieve the synthesis reaction; (2) H2O2 is formed in the gas phase and then solubilised and/or stabilised in the water layer. A global reaction pathway is finally proposed to summarize the synthesis reaction.