The invention refers to a wind turbine blade integrating a lightning protection system. The wind turbine blade comprises one spar cap formed by a plurality of carbon plates stacked together. The wind turbine blade comprises a first down-conductor placed alongside the tip region of the spar cap, and a second down-conductor placed alongside the root region of the spar cap. The first down-conductor extends from the spar cap's tip end towards the spar cap's mid region, and terminates at a first down-conductor's end located adjacent a first region of the spar cap which extends from a cross-sectional area of the spar cap which area is equal or higher than 75% of the maximum cross-sectional area of the spar cap, being that area the one closest to the spar cap's tip end, to a cross-sectional area of the spar cap which area is 100% of the cross-sectional area of the spar cap, being that 100% of the cross-sectional area the one closest to the spar cap's root end.