Here, the synthesis conditions involved in the obtention of magnesium hydroxide [Mg(OH) 2 ] nanoparticles by hydrothermal route are studied. The aim is to control the characteristics of the products only by setting the correct reaction conditions. In addition, they have simplified the method by using simpler equipment in the synthesis and eliminating any further purification processes to obtain pure Mg(OH) 2 particles in a scalable, safe, and economic process. They present the role of the treatment temperature by means of differential scanning calorimetry, water/ magnesium oxide ratio, ageing time, and temperature increase rate and the characteristics of the resulting Mg(OH) 2 particles. Characterisation of the products was carried out by X-ray diffraction, dynamic light scattering, scanning electron microscopy, and transmission electron microscopy.