The present disclosure relates to a lithium secondary battery using lithium titanium oxide (LTO) as a negative electrode active material. More specifically, the present disclosure relates to a secondary battery having improved input and output characteristics through the optimization of the pore ratio of the LTO. The lithium secondary battery including the lithium titanium oxide negative electrode active material according to the present disclosure provides an effect of significantly improved output density through the maximization of reaction active sites with electrolyte due to a porous structure.