A separator for a lithium secondary battery, comprising a polyolefin-based porous substrate; and a coating layer on at least one surface of the polyolefin-based porous substrate, a coefficient of performance Q1 of the polyolefin-based porous substrate as represented by Equation 1 is greater than or equal to 1.2 (gf/nm·μm), a coefficient of performance Q2 of the polyolefin-based porous substrate as represented by Equation 2 is greater than or equal to 0.25 (gf/nm·%), and the coating layer includes a binder and inorganic particles: Q 1 = P gf S nm × T μm Q 2 = P gf S nm × R % wherein, in Equations 1 and 2, P is a puncture strength of the polyolefin-based porous substrate, measured by preparing ten specimens by cutting the separator into a width of 50 mm × a length of 50 mm at 10 different points, placing on a 10 cm hole by using a KES-G5 equipment (Kato Tech Co., Ltd.), and then, measuring three times with respect to a force with which each specimen is punctuated, while pressed with a 1 mm probe, and the three measurements per specimen averaged, S is an average pore diameter of the polyolefin-based porous substrate, measured according to ASTM F316-03, T is a thickness of the polyolefin-based porous substrate, R is a porosity of the polyolefin-based porous substrate, measured by obtaining a volume using a thickness and an area of the separator, measuring a weight thereof, and reflecting specific gravity (0.95 g/cm 3 ) of high density polyethylene and expressed as vol%, wherein a puncture strength standardized by the thickness of the polyolefin-based porous substrate is greater than or equal to 0.4 N/μm. a polyolefin-based porous substrate; and a coating layer on at least one surface of the polyolefin-based porous substrate, a coefficient of performance Q1 of the polyolefin-based porous substrate as represented by Equation 1 is greater than or equal to 1.2 (gf/nm·μm), a coefficient of performance Q2 of the polyolefin-based porous substrate as represented by Equation 2 is greater than or equal to 0.25 (gf/nm·%), and the coating layer includes a binder and inorganic particles: Q 1 = P gf S nm × T μm Q 2 = P gf S nm × R % wherein, in Equations 1 and 2, P is a puncture strength of the polyolefin-based porous substrate, measured by preparing ten specimens by cutting the separator into a width of 50 mm × a length of 50 mm at 10 different points, placing on a 10 cm hole by using a KES-G5 equipment (Kato Tech Co., Ltd.), and then, measuring three times with respect to a force with which each specimen is punctuated, while pressed with a 1 mm probe, and the three measurements per specimen averaged, S is an average pore diameter of the polyolefin-based porous substrate, measured according to ASTM F316-03, T is a thickness of the polyolefin-based porous substrate, R is a porosity of the polyolefin-based porous substrate, measured by obtaining a volume using a thickness and an area of the separator, measuring a weight thereof, and reflecting specific gravity (0.95 g/cm 3 ) of high density polyethylene and expressed as vol%, wherein a puncture strength standardized by the thickness of the polyolefin-based porous substrate is greater than or equal to 0.4 N/μm. <EOS>