The present invention relates to: a negative active material for secondary batteries which comprises a silicon oxide-based composite material, attains a high battery capacity, and has excellent charge / discharge cycling characteristics; a process for producing the negative active material; and a negative electrode and a lithium-ion battery both obtained using the negative active material. The silicon oxide-based composite material has a new structure and is directly obtained by burning, in an inert gas atmosphere, a polysilsesquioxane having a specific structure. The yielded silicon oxide-based composite material has graphitic carbon and is represented by the general formula SiOxCy (0.5<x<1.8, 1<y<5). In an examination by the X-ray small-angle scattering method, the composite material gives a spectrum which shows scattering in the range of 0.02 Å-1<q<0.2 Å-1. In an examination by Raman spectroscopy, the composite material gives a spectrum which shows scattering at 1,590 cm-1 (G band; graphite structure) and at 1,325 cm-1 (D band; amorphous carbon), the peak intensity ratio of crystalline carbon and amorphous carbon (ID / IG ratio) being in the range of 2.0-5.0. The silicon oxide-based composite material is used as a negative active material to form a negative electrode therefrom, and the negative electrode is used to form a lithium-ion secondary battery.