The present invention relates to a porous sheet comprising cellulose fibers having an average fiber diameter ranging from 20 to 500 nm; cut fibers having an average fiber diameter ranging from 1.5 to 20 μm; and a hydrophilic polymer binder, wherein an amount of the cut fibers is 1% by weight or more and 80% by weight or less based on the total weight of the cellulose fibers and the cut fibers, and an amount of the hydrophilic polymer binder is 5 parts by weight or more and 30 parts by weight or less with respect to 100 parts by weight of the total weight of the cellulose fibers and the cut fibers. The porous sheet of the present invention can exhibit a superior strength (in particular, both tear strength and tensile strength), and exhibits a superior performance as a separator for an electrochemical device.