A lithium-ion secondary battery includes a positive electrode, a negative electrode containing an active material, and an electrolytic solution, in which the active material contains, as constituent elements, Si, O, and at least one element M1 selected from Li, C, Mg, Al, Ca, Ti, Cr, Mn, Fe, Co, Ni, Cu, Ge, Zr, Mo, Ag, Sn, Ba, W, Ta, Na, and K, and the atomic ratio x (O/Si) of O to Si is 0.5≦x≦1.8.