<p>Currently, nanoparticles with enhanced biological and electrochemical property prepared via cost-effective methods receive more attention. In this context, here we have reported cubic structure magnesium oxide nanoparticles (MgO NPs) using extract of <i>Pouteria campechiana</i> (canistel) fruit, and its properties are enhanced by functionalizing the NPs using a natural biopolymer-chitosan. The phytochemical analysis of the fruit extract confirms the presence of various biomolecules, and the NPs functional groups are identified from ATR-FTIR spectrum. The formation of a cubic crystalline phase of both MgOs with average crystallite sizes of 21 and 16&#xa0;nm is evident from the powder X-ray diffraction pattern using the Debye–Scherrer formula. Using UV–visible spectroscopy to examine the optical properties, it was found that when MgO was functionalized with chitosan, the band gap dropped from 5.46 to 4.78&#xa0;eV. Scanning electron microscopy (SEM) was employed for the surface morphological examinations, and the results indicate that both samples are well-prepared and have a combination of polyhedral and spherical shapes. The elemental composition was confirmed by the EDAX analysis. The elements’ chemical states in the developed nanoparticles were examined using X-ray photoelectron spectroscopy (XPS). The antibacterial performance of the pure and chitosan-modified MgO NPs is examined against <i>Bacillus subtilis</i> and <i>Pseudomonas aeruginosa</i> at various concentrations. Pseudocapacitive behavior of the electrode was studied from cyclic voltammogram at different scan rates (5, 10, 25, 50, 75, and 100&#xa0;mV&#xa0;s⁻¹). The specific capacitance was obtained from galvanostatic charge–discharge profile with highest value of 56.32 Fg⁻¹ at 0.5 Ag⁻¹ for chitosan-modified MgO NPs than bare – MgO (37.83 Fg⁻¹). These results highlight the enhanced property of chitosan-functionalized MgO NPs as a promising electrode for supercapacitor applications.</p> Graphical Abstract <p></p>