The present disclosure relates to a method for manufacturing a crosslinked structure-containing separator for a lithium secondary battery, including the steps of: preparing a polyolefin porous support including a photoinitiator; and irradiating ultraviolet rays to the polyolefin porous support, wherein the polyolefin porous support has a BET specific surface area of 10-27 m2/g, and the content of the photoinitiator is 0.01-1.0 mg/m2 based on the specific surface area of the polyolefin porous support. The present disclosure also relates to a crosslinked structure-containing separator for a lithium secondary battery obtained from the method, and a lithium secondary battery including the crosslinked structure-containing separator for a lithium secondary battery. The polyolefin porous support has a controlled BET specific surface area so that it may be crosslinked even with a small amount of photoinitiator.