Colloidal suspension of NiGa2O4 nanoparticles was synthesized by gel-sol method. Starting from an aqueous solution of Ni(NO3)2·6H2O, Ga(NO3)3·nH2O and a β-diketone ligand (acetylacetone), a precursory hydrogel was obtained through an epoxide-mediated alkalization. Then, a mild thermal treatment at 80 °C induces the deflocculation of the hydrogel, resulting in the formation of NiGa2O4 nanoparticles which is stably suspended in a solvent. The formation mechanism of the colloidal suspension was closely studied, revealing that chelation of acetylacetone to Ni cation with the formation of NiGa2O4 nanoparticles plays a key role to impart dispersion stability.