Although no evident hydrogen-bond network appears, an ultrahigh proton conductivity of 2.91 × 10-2 S cm-1 at 363 K and 90% RH with an ultralow activation energy of 0.10 eV was observed in an anionic lanthanide-organic framework Na2[Eu(SDB)2(COO)]·0.375DMF·0.4H2O (1); both values approach the records among all reported proton-conducting MOF materials. This suggests that the proton conduction process in 1 is reminiscent of the Grotthuss mechanism, which together reveals an effective proton transportation pathway associated with aligned Na+ and their coordinated water.