Simultaneous improvement in adsorption selectivity and capacity for single adsorbents is challenging but counting for much in adsorptive separations. To this end, a formate metal-organic framework and activated carbon fiber composite was synthesized in our work by a simple two-step process, involving homogeneous precipitation of a MOF precursor on an activated carbon fiber and subsequent template replication. The resultant core-shell composite, ACF@[Ni3 (HCOO)6 ], exhibited optimized adsorption performance both in selectivity and capacity for the separation of CH4 /N2 to most of state-of-the-art adsorbents.