Abstract <p>Magnesium oxide (MgO) nanopowders were synthesized by an ultrasonic-assisted solution combustion synthesis route using magnesium nitrate as oxidizer and sucrose as fuel. The influence of ultrasonic pretreatment and fuel-to-oxidizer ratio on the phase composition, microstructure, surface area, particle size distribution, and dispersibility of the resulting MgO powders was systematically investigated. X-ray diffraction analysis confirmed the formation of single-phase cubic MgO for all samples. Compared to conventional solution combustion synthesis, ultrasonic pretreatment led to a pronounced reduction in crystallite size and particle agglomeration, accompanied by a significant increase in specific surface area. Under optimized conditions, MgO nanopowders with a high specific surface area of approximately 340 m² g^–1 and a narrow particle size distribution were obtained. The improved microstructural characteristics were attributed to cavitation-induced modification of precursor chemistry and more homogeneous combustion reactions. In addition, the functional properties of the synthesized MgO nanopowders were evaluated through antibacterial activity tests, demonstrating their potential applicability in advanced inorganic and functional materials.</p>