The hydrolysis behavior of ZrB2 powder during attrition milling was studied in de-ionized water and ethanol. Surface characterization, thermal analysis, chemical analysis and electron microscopy were utilized to analyze the surface properties of as-milled powders. The results proved that the surface of ZrB2 powder was mainly composed of Zr–O, B–O and B–OH bonds as hydrolysis proceeded, and the amount of surface B–O bond was found to increase rapidly in water, suggesting a more B2O3-like surface behavior were developed. Results also showed when milled at 300 rpm for 4 h in water, 64.45 at% of B was in the form of B2O3 at a thickness of ∼3 nm from the surface. The nano-sized surface Zr–B–O oxide layer (∼5 nm in thickness) could help to improve the dispersion of powder in aqueous media.Highlights► The surface was mainly covered of Zr–O, B–O and B–OH bonds after hydrolysis. ► ZrB2 powder tended to behave like a B2O3-modified surface by milling treatment. ► The surface B/Zr atomic ratio decreased from water to ethanol medium. ► The nano-sized oxide layer (∼5 nm) was observed and helped to improve the dispersion of ZrB2 particles in dilute aqueous media.