The present invention relates to a negative electrode material for nonaqueous electrolyte secondary batteries, which is composed of a silicon composite body that has a structure wherein microcrystals or fine particles of silicon are dispersed in a substance having a composition different from that of the microcrystals or fine particles, said silicon composite body having a crystallite size of the microcrystals or fine particles of 8.0 nm or less as calculated using Scherrer's equation on the basis of the half width of the diffraction peak belonging to Si(220) in an X-ray diffraction. The present invention is able to provide a negative electrode material for nonaqueous electrolyte secondary batteries, which has excellent coulombic efficiency, and a nonaqueous electrolyte secondary battery.