A novel photochemical reactor is developed and is used to oxidize elemental mercury (Hg-0) from flue gas by ultraviolet (UV)/H2O2 process. The effects of several parameters on Hg-0 removal were investigated. The reaction mechanism of Hg-0 removal is also proposed. The results indicate that 254 nm is the most effective wavelength for Hg-0 removal. When UV energy density per unit solution increases from 0 to 0.0056 W/mL, Hg-0 removal efficiency increases from 11.7% to 85.1%. Hg removal efficiency increases from 59.4% to 85.1% when H2O2 concentration increases from 0 to 0.50 mol/L, but reduces from 85.1% to 77.3% when H2O2 concentration further increases from 0.50 to 1.0 mol/L. With solution pH increasing from 1.21 to 10.01, Hg-0 removal efficiency sharply reduces from 88.2% to 54.0%. Increasing O-2 concentration (0-12.0%) makes Hg-0 removal efficiency greatly increases from 59.4% to 87.6%. Solution temperature only has a small impact on Hg removal. Hg2+ is the final reaction product of Hg-0 removal, and Hg-0 is removed by the oxidations of H2O2, 'OH, 'O, O-3 and the photoexcitation of UV. (C) 2014 Elsevier B.V. All rights reserved.