Provided is a separator for an electrochemical device, including: a porous polymer substrate; and a porous organic/inorganic coating layer formed on at least one surface of the porous polymer substrate and including heat conductive inorganic particles and core-shell particles, wherein the particles are bound to one another by a binder polymer, and wherein the core-shell particle includes a core portion and a shell portion surrounding the surface of the core portion, the core portion includes a metal hydroxide having heat-absorbing property at 150-400° C., the shell portion includes a polymer resin, and the polymer resin is a water-insoluble polymer or crosslinked polymer. An electrochemical device including the separator is also provided. It is possible to provide a separator with an improved heat-absorbing effect and safety, and an electrochemical device including the same.