A separator for secondary batteries, including: a separator substrate having at least one surface, wherein the separator substrate includes a polyolefin-based polymer resin having a porous structure and a coating layer is applied to one surface or opposite surfaces of a separator substrate made of a polyolefin-based polymer resin having a porous structure, wherein the coating layer includes a thickener, a filler, a particle-type binder, and a dissolution-type binder, wherein the thickener comprises carboxymethyl cellulose, and wherein an amount of the particle-type binder is greater than an amount of the dissolution-type binder.