A simple polyol method was developed to synthesize uniform sphere-like Co 3 O 4 nanocrystals in ethylene glycol. Powder X-ray diffraction (XRD) and electron diffraction (ED) showed that the as-prepared sample was indexed as the cubic spinel structure. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated that the Co 3 O 4 nanocrystals were spherical with the crystallite size in the range of 90–110 nm. Infrared spectra and Raman spectra confirmed the formation of the Co 3 O 4 nanocrystals. The magnetic properties of the Co 3 O 4 nanocrystals were measured by using a superconducting quantum interference device (SQUID) magnetometer, which showed that the as-prepared sample exhibited a tiny hysteresis loop with the magnetization value of 2.4 emu/g and the coercivity of 110 Oe.