The influence of H2O2 on the photo-reductive precipitation of Eu(3+) from a solution containing Sm(3+), Eu(3+) and Gd(3+) was investigated. The solution contains isopropanol as a reduction agent, ammonium sulfate as a precipitation agent, and hydrogen peroxide as an acceleration agent of precipitation rate. A mercury lamp emitting a wavelength of 254 nm was used as a light source. Adding a small amount of H2O2 considerably increased the photo-reductive precipitation rate of Eu(3+). OH radicals obtained from the photodecomposition of H2O2 oxidized isopropanol into the radical (CH3)2CㆍOH and the resulting radicals reduced Eu(3+) rapidly. It was found that the organic radical has the ability to reduce only Eu(3+) in the solution containing Sm(3+), Eu(3+) and Gd(3+). The precipitation yields of Eu, Sm and Gd were about 99%, 10% and 4%, respectively. It was also found that the Sm and Gd were not photo-reduced and co-precipitated with Eu.