A flexible and highly conducive nylon porous membrane (NPM)/nickel (Ni) composite film with outstanding electromagnetic interference (EMI) shielding performance is fabricated via a facile electroless deposition method. The NPM, with a large specific surface area, is amenable to the electroless deposition of Ni and the enhancement of interaction between Ni and NPM. Highly conducive Ni layers are uniformly deposited on the upper and lower surfaces of NPM to construct a sandwich structure that provides numerous interfaces to reflect, scatter, and absorb electromagnetic waves. The resultant NPM/Ni film exhibits an ultra-high EMI shielding effectiveness (EMI SE) of 77 dB with a film thickness of only 100 mu m. Moreover, the NPM/Ni film shows cyclic EMI shielding stability under repeated mechanical deformation, with 85% retention after 300 bending cycles. Our work provides an effective approach to fabricate reliable metal-polymer composite films that show potential for applications in EMI shielding.