We carried out a Sm-Nd isotopic reconnaissance study of South Korea. Eight river sediments gave crustal residence ages (TDM) between 1.7 and 2.7 Ga, implying that, on average, the crust of South Korea was formed in Early to Middle Proterozoic time. Twenty-six Precambrian basement rocks yielded TDM between 1.4 and 3.8 Ga. More than half of them exceed 2.5 Ga, indicating that South Korea has a long history of crustal evolution. Four of the samples have TDM from 3.2 to 3.8 Ga suggesting the possibility that there may be ancient continental crust in Korea having ages comparable to those of the oldest cratons in the world. However, these samples also have preferentially higher Sm/Nd, so their old ages could be artifacts, thus requiring confirmation. The large variation in TDM of South Korea is reminiscent of that for the South China block. However, the existence of Early Archean ages better matches that of the North China block, because the basement of south China was thought to be mostly Proterozoic in age. The recent discovery of rare Archean basement rocks in the South China block may favor models that attempt to correlate South Korea with south China.