The electrical properties of a highly oriented crystalline MOF nanofilm were studied. This nanofilm has low activation energy and a proton conductivity that is among the highest value reported for MOF materials. The study uncovered the reasons for the excellent performance of this nanofilm and revealed a new pathway for proton transport in MOF materials; besides the channels inside a MOF, the surface of the MOF nanocrystal can also dominate proton transport.