The dispersion of highly concentrated Zirconium diboride (ZrB2) suspension in aqueous media was investigated in terms of zeta potential and rheological measurements, with a salt of polyacrylate polymer (SD-07) as dispersant. The adsorption behavior of SD-07 on ZrB2 particle surface was also studied. Results showed that acid cleaning improved the fluidity of aqueous ZrB2 slurry. Concentrated (up to 50 vol%) and well-stabilized suspension was obtained in the alkaline pH region, with 0.60 mg/m2 SD-07. On this basis, 50 vol% ZrB2 gelcasting slurry was prepared. The linear shrinkage and flexural strength of as-casted green body were (3.42 ± 0.13)% and (9.4 ± 0.3) MPa, respectively.