Abstract: Provided is a negative electrode active material for a lithium-ion secondary battery, comprising SiOx that has an intensity ratio A1/A2 of 0.1 or less in spectra measured by a Fourier transform infrared spectrometer after subjecting the SiOx to evacuation treatment at 200° C., given that A1 designates an intensity of a silanol group-derived peak which appears around 3400 to 3800 cm?1, and A2 designates an intensity of a siloxane bond-derived peak which appears around 1000 to 1200 cm?1. It is preferred that x in the SiOx satisfies x<1; there is no sign of an Si—H bond-derived peak A3 that may normally exhibit around 2100 cm?1 in spectra of the SiOx measured by a laser Raman spectrometer; and a ratio Y/X is 0.98 or less, given that X is a mole ratio of O to Si in the whole body of the SiOx, and Y is a mole ratio of O to Si in a surface vicinity of the SiOx. A lithium-ion secondary battery having high initial efficiency and charge/discharge capacity can be obtained by using this active material.