The present invention relates to a negative electrode active material comprising a mixture of a first negative electrode active material and a second negative electrode active material, wherein the first negative electrode active material has a hardness of 1 kg/mm2 to 10 kg/mm2 on the basis of the Vickers hardness standard, and the second negative electrode active material has a higher hardness than the first negative electrode active material. The negative electrode active material according to the present invention comprises a mixture of negative electrode active materials having different hardness so that pores of an active material layer are maintained in spite of a rolling process at the time of producing an negative electrode, and the pores acting as an electrolyte flow passage of an electrode can effectively be secured, thereby producing a lithium secondary battery having excellent battery performance by lowering resistance when a battery is charged or discharged.