Currently, serious energy crises, as well as global warming, are becoming major problems. Therefore, there is an urgent need to develop effective and reliable energy storage devices. The development of supercapacitors is one of the best and most efficient energy storage technologies due to their eco-friendly nature, fast charge-discharge time, high power density, and high energy density. In this work, using the Co-precipitation method, pure Co3O4 and Ag/Fe-doped (0.05- 0.25M) Co3O4 nanoparticles were synthesized at 80 °C, and the effect of Ag/Fe doping on some physical properties of Co3O4 nanoparticles was examined. The aim of this work could be to develop nanostructured (Fe, Ag) doped cobalt oxide (Co3O4) materials for high capacitive supercapacitor applications. The XRD results revealed the formation of single cubic phase Co3O4 nanoparticles with an average crystallite size of 19.37 nm, 14.09 nm, and 12.98 nm for pure Co3O4, 0.25M Fe-doped Co3O4, and 0.25M Ag-doped Co3O4 nanoparticles, respectively. Morphological examinations indicated that un-doped Co3O4, 0.25M Fe-doped Co3O4, and 0.25M Ag-doped Co3O4 have porous structures with sponge-like, porous structures with small cracks /holes and flower-like porous structures, respectively. Pure Co3O4, 0.25M Fe-doped Co3O4, and 0.25M Ag-doped Co3O4 nanoparticles have BET surface areas of 53.06 m 2 /g, 351.56 m 2 /g, and 407.338 m 2 /g, respectively. The band gap energy values of Co3O4 nanoparticles were 2.96 eV, with an additional sub-band gap energy of 1.95 eV. Moreover, the band gap energy values Fe–doped Co3O4 nanoparticles were found to be between 2.4 and 2.54 eV with an additional sub-band corresponding to energies varying between 1.46 and 1.93 eV for all samples. Whereas, the band gap energy values of Ag–doped Co3O4 nanoparticles were found to be between 2.22 and 2.75 eV with an additional sub-band corresponding to energies varying between 1.43 and 1.94 eV for all samples. The presence of M−O bonds (M = Co, Fe, and Ag) was analyzed by FTIR spectroscopy. The doped Co3O4 shows improved thermal properties owing to the doping effect of iron and silver. The CV test revealed that, 0.25M Fe–doped Co3O4 and 0.25M Ag–doped Co3O4 nanoparticles sample exhibited highest specific capacitance value of 992.7F/g and 588.5 F/g at 5mV/s, respectively. Moreover, the energy density and power density of the 0.25M Fe-doped Co3O4 and 0.25M Ag-doped Co3O4 nanoparticles were 9.17 Wh/kg, 472.1 W/kg, and 27.9 Wh/kg, 3816.1 W/kg, respectively. These results suggest its potential application in energy storage devices. Keywords: Doping, Cobalt Oxide nanoparticles, Co-precipitation method, Supercapacitor