A separator for a rechargeable lithium battery and a rechargeable lithium battery including the same, the separator including a substrate, and a heat-resistant porous layer on at least one side of the substrate, the heat-resistant porous layer including a crosslinked binder and a non-crosslinked binder, wherein the crosslinked binder has a cross-linked structure of at least one crosslinkable compound, the at least one crosslinkable compound including a multi-functional urethane-based compound, and the crosslinked binder and the non-crosslinked binder are included in a weight ratio of about 3:7 to about 8:2.