South Korea has investment agreements such as FTAs, BITs with several countries. Up to now, no single case has been registered against the Korean government on breach of investment agreements, but it is likely that the number of such cases would increase. Therefore, an investor-state dispute settlement system, an arbitral procedure by which a foreign investor may seek compensation of damage against the host country, is gaining its importance. The provision of the ISDS has been one of the hottest issues in Korea while the Kor-US FTA was being signed. In this respect, with the growing number of regional agreements such as BITs and FTAs, a careful scrutiny on the ISDS is necessary for Korea. I have therefore studied theoretically subjects including the National Treatment(NT), the Most-Favored Nation(MFN), Fair and Equitable Treatment and Expropriation - those that have been the objects of protection on investors. And I have analyzed ICSID arbitral awards and provided implications. In the ICSID arbitral awards, the Fair and Equitable Treatment turned out to be the most recognized violation on investors by the host State in terms of investor protection. On the other hand, Indirect Expropriation - a matter of which public anxiety was shown led by civic groups - was not generally recognized in arbitral awards. This study is written for sake of governments, local autonomous entities and public enterprises that are in charge of FTAs and BITs.