The Co-doped BiFeO3 (5, 10, 20 and 30 mol%) nanoparticles were successfully synthesized via a simple solution method. The influence of the Co-doping on their nanostructures, magnetic and electrochemical properties was studied. An investigation of the magnetic properties revealed the enhancement of ferromagnetic properties with the Co doping content. Improvement of magnetization (0.21–9.24 emu/g) and coercivity (52.85–17970.57 Oe) of the nanoparticles could be attributed to the increasing of the Co content (which causes a decreasing of particle size), temperature dependence and the presence of impurity phases. Additionally, the electrochemical properties of the electrodes were studied by Cyclic Voltammetry (CV), Galvanostatic Charge-Discharge (GCD) and Electrochemical Impedance Spectroscopy (EIS). The Co doping contents caused a decreasing of the specific capacitances and the capacity retention, except for the 5 mol% of Co-doped BiFeO3, which the capacity retention is at the highest of 62% after 500 cycles at 10 A/g.