Co3O4 nanoparticles have been prepared for the first time via reflux method, as an alternative low-temperature high-yield process, starting from one single precursor. A plausible mechanism is suggested for the synthetic process. XRD, TEM, FTIR and VSM were used for the structural, morphological, spectroscopic, and magnetic characterization of the product respectively. X-ray diffraction line profile fitting showed that average particle size of the sample is 28 nm. Morphology of the synthesized powder was observed to be thin nanosheets with a thickness of 2-3 nm based on SEM and TEM analyses. Magnetic measurements showed a deviation of the Neel temperature from the bulk value which is attributed to the finite size effects. A loop shift with an enhanced coercivity is observed in the field-cooled hysteresis loops. The opening of the hysteresis loop reveals the existence of the spin-glass like surface spins of the Co3O4 nanoparticles.