In the water-in-oil (W/O) microemulsions based on nonionic surfactants, i.e., Brij 30, Brij 56, or Triton X-100, the omega value (molar ratio of water to surfactant), anion, and surfactant could remarkably affect the radiolytic reduction of Cu2+ and the morphologies of the reduction products simultaneously. The addition of toluene or naphthalene could transform the reduction products from copper to cuprous oxide in the Brij 56-based microemulsion, and the efficiency of naphthalene was obviously higher than that of toluene. After the effects of pH value and cosurfactant were excluded. it could be concluded that the effects of the omega value, the anion, and the structure of the surfactant on the yield of hydrated electrons (e(aq)(-)) play a key role in the radiolytic reduction of Cu2+. It was also suggested that the morphology of the reduction product may be controlled by the yield of e(aq)(-). (c) 2007 Elsevier Inc. All rights reserved.