We measure the top quark mass (mt) in p¯p collisions at a center of mass energy √s=1.96 TeV using dilepton t¯t→W+bW−¯b→ℓ+νℓbℓ−¯νℓ¯b events, where ℓ denotes an electron, a muon, or a tau that decays leptonically. The data correspond to an integrated luminosity of 5.4 fb−1 collected with the D0 detector at the Fermilab Tevatron Collider. We obtain mt=174.0±1.8(stat)±2.4(syst) GeV, which is in agreement with the current world average mt=173.3±1.1 GeV. This is currently the most precise measurement of mt in the dilepton channel.Received 28 April 2011DOI:https://doi.org/10.1103/PhysRevLett.107.082004© 2011 American Physical Society