The present invention intends to provide silicon-containing particles that, when used as a negative electrode active material for a nonaqueous electrolyte secondary battery, can form a nonaqueous electrolyte secondary battery that is less in volume change during charge/discharge and has high initial efficiency and excellent cycle characteristics. The present invention provides silicon-containing particles that are used as a negative electrode active material for a nonaqueous electrolyte secondary battery and have a diffraction line with a peak at 2&thetas;=28.6° in X-ray diffractometry, a negative electrode material for a nonaqueous electrolyte secondary battery therewith, a nonaqueous electrolyte secondary battery, and a method of manufacturing the silicon-containing particles.