The Jeju Special Self-Government Provincial Government(JSSPG) made the plan penetrating gradually electric vehicles(EVs) in the Jeju Special Self-Government Province(Jejudo). However the effects of EVs penetration on the electrical grid of the Jejudo are not yet presented. In this paper the yearly electric energy consumed by the EVs in the Jejudo was calculated for the future 10 years and the possible number of EVs to be able to introduce under the present electric energy supply system presented, and we hope that the results are to be a help to governors realizing the EVs penetration plan. And we could increase the correctness in estimating electric energy consumed by EVs through using the fuel economy formally expressed in U.S.A. and Korea. The calculation results show that the rate of the electric energy used by the EVs will become to 2.9% at its maximum at the 2017 year when the penetration rate of EVs in passenger cars becomes 10%, and the rate of the electric energy consumed by the EVs will become to 9.4% at its maximum at the 2020 year when the penetration rate of EVs in passenger cars becomes 30%. The whole electric energy supply system of the Jejudo has a power capacity to be able to supply EVs electric energy for the time being if we use a proper electric energy fee system, and the supply cost of electric energy can be decreased through penetrating EVs.