Disclosed is a separator for an electrochemical device including a porous polymer film, and a porous coating layer including at least one type of particles of inorganic particles and organic particles and binder polymer, the porous coating layer formed on one surface or both surfaces of the porous polymer film, wherein the porous polymer film has a structure in which multiple fibrils arranged parallel to the surface of the film are stacked in layers, and a diameter of the fibril disposed at the side of one surface of the film where the porous coating layer is formed is smaller than a diameter of the fibril disposed at a central part in a thickness-wise direction of the film, and an electrochemical device comprising the same.