The electrochemical behavior of CoCl2 in 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF6) was investigated by cyclic voltammetry. The cyclic voltammograms were obtained from electrochemical measurement under different temperatures, and the reversible behavior for Co2+/Co3+ redox couple on glassy carbon electrode in [bmim]PF6 was confirmed by the characteristic of the peak currents. The diffusion coefficients (about 10-11m2/s) of Co2+ in [bmim]PF6 under different temperatures were evaluated from the dependence of the peak current density on the potential scan rates in cyclic voltammograms. It is found that the diffusion coefficient increases with increasing temperature. Diffusion activation energy of Co2+ in [bmim]PF6 is also calculated to be 23.4kJ/mol according to the relationship between diffusion coefficient and temperature.