| We investigate the adsorption properties of Na atoms on graphenes using the first-principles method of density functional theory combined with the pseudopotential approximation. Three types of graphenes have been mainly considered: intrinsic graphene, B-doped graphene and N-doped graphene. The results indicate that two types of graphenes, i.e. doped with B and N to replace C atoms, exhibit prodigious differences from the intrinsic graphene in terms of the adsorption energy, charge density, density of states and Na storage capacity on graphenes. The adsorption energy of Na on B-doped graphene is -1.93 eV, which is over 2.7 times that of Na on the intrinsic graphene, while the N-doped graphene has a higher adsorption energy than the intrinsic graphene. Moreover, the orbital hybridizations can be observed in the B-doped graphene, while there is no evidence of orbital hybridization in the intrinsic or N-doped graphenes. Each B atom can adsorb up to three Na atoms, which is larger than that of intrinsic and N-doped graphenes. Therefore, B-doped graphene is expected to be novel materials for storing Na.