Double perovskites La2NiRuO6 and La2ZnRuO6 were studied by use of the density functional method. The unquenched orbital moments were found for both Ni and Ru after spin-orbit coupling effect is included. Electron correlation U is found to be important in reproducing the experimental results. Both compounds are found to be half metallic when U of Ru is less than 1.36 eV, but they are semiconductors for larger U, in agreement with the experimental observation. This reveals that the semiconducting behavior is primarily driven by the electron correlation U. Crown Copyright (C) 2010 Published by Elsevier B. V. All rights reserved.