The oscillation frequency, md, of B0 mesons is measured using semileptonic decays with a D or D meson in the final state. The data sample corresponds to 3.0fb1 of pp collisions, collected by the LHCb experiment at centre-of-mass energies s = 7 and 8TeV. A combination of the two decay modes gives md=(505.0±2.1±1.0)ns1, where the first uncertainty is statistical and the second is systematic. This is the most precise single measurement of this parameter. It is consistent with the current world average and has similar precision.
