Negative electrode active material containing oxygen-containing silicon material, and method for producing same

Provided are: a negative electrode active material which contains a silicon material and makes it possible to modify the capacity maintenance rate of a secondary battery to a suitable value; and a method for producing the negative electrode active material. A negative electrode active material characterized by containing an oxygen-containing silicon material having an oxygen content (WO %) of 16 to 27% by mass exclusive (i.e., 16 < WO < 27) and a silicon content (WSi %) of 62 to 81% by mass exclusive (i.e., 62 < WSi < 81).