A two-step reduction route is proposed for well-dispersed submicrometer ZrB2 powder synthesis with low oxygen content. The second synthesis step can reduce the oxygen content apparently, whereas presents minor adverse effects on particle size and dispersion of ZrB2 powders. The samples were mainly characterized by an oxygen-nitrogen analyzer and X-ray diffractometer (XRD). It can be determined that the adsorbed oxygen constitutes a low proportion of total oxygen content based on the release profile of oxygen and nitrogen contents. Besides, the oxygen content calculated based on XRD characterization is significantly lower than the total oxygen content measured by impulse-thermal conductivity. Furthermore, the lattice constants were determined according to XRD patterns as being higher than the calculated theoretical values based on the First-Principles, indicating that a portion of oxygen remains in ZrB2 powders in the form of interstitial impurity atoms.