The present invention provides a negative electrode active material for a secondary battery, the negative electrode active material including a core that includes a lithium titanium oxide and a surface treatment layer located on a surface of the core, wherein the surface treatment layer includes a boron-containing lithium oxide at an amount that allows a boron content to have a molar ratio of 0.002 to 0.02 with respect to 1 mole of the lithium titanium oxide, and when 2 g of the negative electrode active material is titrated at pH 5 or lower using 0.1 M HCl, a titrated amount is 0.9 to 1.5 ml, and a secondary battery including the same. The negative electrode active material exhibits an excellent capacity recovery rate and an output characteristic when applied to a battery and is capable of reducing gas generation by preventing electrolyte decomposition.