In this paper, characteristics of electron parameters of SF6/O-2 and inert gas mixture in a capacitively coupled plasma were studied. Here, gases such as He, Ar, and Xe were added to SF6/O-2 mixture and electron energy probability functions (EEPFs) were measured. The electron parameters were acquired, which agreed well with EEPF behaviors. Normally, the inert gas functioned as an electron source and the electron density tended to increase. When the inert gas ratio exceeded other gases, the effect of the mixture varied on each gas. He showed its unique behaviors with the increase in electron temperature. Ar and Xe showed consistent behaviors with increasing electron density and decreasing electron temperature as the inert gas proportion increases. Different behaviors of the electron parameters in inert gases can be explained by the complex contribution of electron attachment of SF6 and the ionization rate of each inert gas.