Abstract: We consider a U(1)′ supersymmetric seesaw model in which a right-handed sneutrino is a thermal dark matter candidate whose relic density can be in the right range due to its coupling to relatively light Z˜′$$ \tilde{Z}^{\prime } $$, the superpartner of the extra gauge boson Z′. Such light Z˜′$$ \tilde{Z}^{\prime } $$ can be produced at the LHC through cascade decays of colored superparticles, in particular, stops and sbottoms, and then decay to a right-handed neutrino and a sneutrino dark matter, which leads to lepton flavor violating signals of same/opposite-sign dileptons (or multileptons) accompanied by large missing energy. Taking some benchmark points, we analyze the opposite- and same-sign dilepton signatures and the corresponding flavour difference i.e., (2e − 2μ). It is shown that 5σ signal significance can be reached for some benchmark points with very early data of ∼ 2 fb−1 integrated luminosity. In addition, 3ℓ and 4ℓ signatures also look promising to check the consistency in the model prediction, and it is possible to reconstruct the Z˜′$$ \tilde{Z}^{\prime } $$ mass from jjℓ invariant mass distribution. © 2015, The Author(s).