The magnesium oxide (MgO) nanoparticles with the morphologies of globular agglomerates were synthesized from a seawater bittern by a wet decarboxylation/precipitation method. The effect of the synthesis parameters on the morphological structure of the MgO nanoparticles prepared was investigated with reaction time and precipitate (NaOH) concentration. It was possible to produce the morphologies of globular agglomerates for MgO nanoparticles. It has an effect on the enlargement size of the MgO nanoparticles. The morphological and physical-chemical properties of the nanoparticles have been characterized by XRD, XRF and FE-SEM. These synthesis conditions by the wet decarboxylation/precipitation method can be applied to synthesize MgO nanoparticles in an industrial plant using other raw materials.