The existence of Majorana neutrinos must lead to lepton-number violating processes, and the Majorana nature of neutrinos can only be experimentally verified via lepton-number violating processes. We study an approach to search for Majorana neutrinos at future electron-positron colliders by exploiting this feature. We investigate ∆ L = 2 like-sign dilepton production and find that lepton colliders with different center-of-mass (c.m.) energies have comparative advantages in resonant production of a Majorana neutrino in both light and heavy neutrino mass range. At the future Circular Electron-Positron Collider (CEPC), with 250 GeV c.m. energy and 5 ab-1 integrated luminosity, we find that there could be more significant sensitivity for resonant production of a Majorana neutrino in the mass range of 30-50 GeV than previous results at LEP2 or LHC. At the 1 TeV ILC with 1 ab-1 integrated luminosity, the sensitivity can be improved for neutrino mass in the range of 450-600 GeV.