The nanoparticles of magnesium oxide used mainly for additives were synthesized through precipitation method in the presence of precipitants. The effects of preparation parameters, such as NaOH and Ca(OH)(2) concentrations, dilution rate, rotation speed on size and morphology of the nanoparticles were investigated. The magnesium oxide was produced from magnesium hydroxide in the waste-seawater bittern. The properties of the obtained nanoparticles were analyzed by XRD and SEM. The obtained magnesium oxide crystals showed a wide distribution of globular structure including sphere or cubic-like morphology. Also size and crystallinity of magnesium oxide crystals increased from 50 to 180nm with increasing a rotation speed.