Bilateral Investment Treaty has a treatment clause on investor and investment which include most-favored-nation treatment(MFN) and national treatment(NT) and fair and equitable treatment(F&ET). Among these, MFN applies to the various areas including trade, investment, foreign exchange(currency), intellectual, rights of diplomatic protection and recognition and enforcement of commercial arbitral awards. As of now, most of the economy-related treaties have the MFN clause as one of the fundamental principles. The MFN is a clause in which a grating state promises offering a special privilege to a third state or beneficiary state. The legal problems of MFN arise mainly due to the fact that the MFN clause have a wide range of terms and regulation. Accordingly, it is the right time to look into the types and characteristics of the MFN clause to get a better understanding of it. Recently, there is a case of awards in which the basic treaty of MFN is applied to the investor-state dispute settlement(ISD) of the third party treaties. This means that the basic treaty of MFN can be applied to substantive rights or treatment. MFN-related case is related to the substantive stipulation, which is because the range of application of MFN in BIT is stipulated widely. Therefore,the Award on the clause of MFN turns out to positive or negative depending on the case. The awards should meet the limits of the subject matter. The ways BITéexpresses the limits of the subject matter inlcude ‘in like circumstances; in like situations, in same circumstance; in same situations.’ And the awards become the matter of interpreting BIT at the arbitral tribunal. The interpretations of BIT are based on Vienna Convention on the Law of Treaties(Art.31). If BIT of the third-party applies as the MFN clause, the exisiting BIT can be nullified. The confusing results arise. Consequently, it is advised that Korea should keep the unified position on the MFN Clause in BIT. This is because the MFN clause of BIT Korea is going to enter into applies to the various areas. Such case has an expansible application. It may be that Korea has to limit its expansible application. The situation is similar to the application of the MFN clause in the United States and Canada. The legal establishment of the ISD clause in BIT, host state prefer exhaustion of local remedies and export state international arbitration. However,the ISD clause in the contract of FTA between Republic of Korea and the Unitied States can apply to the international arbitration in various ways. Accordingly,investment contract in BIT entrusts ISD to the principle of private autonomy.