The present invention relates to an optical sheet and a method of assembling a liquid crystal display module that is capable of preventing an inflow of impurities on a backlight unit, thereby minimizing screen staining caused by the impurities. An optical sheet installed between a liquid crystal display panel and a light guide member according to the present invention includes a transparent peeling sheet adhered to the front surface of the optical sheet facing the liquid crystal display panel; and a semitransparent peeling sheet stuck to the rear surface of the optical sheet facing the light guide member.