A one-step straightforward strategy has been developed to incorporate free imidazole molecules into a highly stable metal-organic framework (NENU-3, ([Cu-12(BTC)(8)(H2O)(12)][HPW12O40])center dot Guest). The resulting material Im@(NENU-3) exhibits a very high proton conductivity of 1.82 X 10(-2) S cm(-1) at 90% RH and 70 degrees C, which is significantly higher than 3.16 X 10(-4) S cm(-1) for Im-Cu@(NENU-3a) synthesized through a two-step approach with mainly terminal bound imidazole molecules inside pores. Single crystal structure reveals that imidazole molecules in Im-Cu@(NENU-3a) isolate lattice water molecules and then block proton transport pathway, whereas high concentration of free imidazole molecules within Im@(NENU-3) significantly facilitate successive proton -hopping pathways through formation of hydrogen bonded networks.