Cu(I) impregnated MIL-100(Cr) [denoted Cu@MIL-101(Cr)] is fabricated by a facile method and utilized in mixed matrix membranes (MMMs) for propylene/propane separation. Cu(I) is prepared from a CuCl2 solution via mild reduction process using sodium sulfite as the reducing agent. The filler is incorporated into a polystyrene-bpolybutadiene- b-polystyrene (SBS) block copolymer matrix to form MMMs. As a result, both the permeability and selectivity of propylene/ propane are improved after Cu(I) impregnation. The best performance is obtained for SBS/Cu@MIL-101(Cr) MMM, and these values represent 17% and 54% improvements compared to those of SBS/MIL-101(Cr) MMM, respectively. This result is attributed to the π-complexation of the loaded Cu(I) by propylene gas, indicating that Cu@MIL-101(Cr) with internal Cu(I) and a high pore volume acted as an effective filler to aid propylene/propane separation.