Water pollution from industrial dyes like methylene blue poses severe environmental and health risks, necessitating effective wastewater treatment methods. Among various adsorbents, MgO stands out due to its high surface area, tunable porosity, and superior adsorption capabilities. This research presents the preparation of nano-scale magnesium oxide (MgO) fibers using electrospinning, followed by calcination at temperatures of 300 °C, 400 °C, 500 °C, 600 °C, and 700 °C. The effects of calcination temperatures on MgO's surface characteristics, microstructure, crystalline phases, and adsorption performance were investigated. SEM and TEM analyses revealed that fibers calcined at 500 °C possessed the most distinct porous structure, with a coarse surface and substantial pores, which enhanced adsorption properties. XRD analysis confirmed that the 500 °C calcined MgO fibers had the highest crystallinity, particularly the (200) crystal plane. Notably, BET surface area analysis confirmed the superior adsorption properties of these fibers, making them highly effective for wastewater treatment applications. Adsorption tests for methylene blue (MB) indicated that these fibers achieved a maximum dye removal efficiency of 52.52% and an adsorption capacity of 43.11 mg/g within 90 min. The adsorption process aligned with a quasi-second-order kinetic model (R