Indoleamine 2,3-dioxygenase (IDO) is predicted to be therapeutic target for treatment of cancer and immune disease. Thus, we examined methanol extracts prepared from 156 Korean local plants for their inhibitory effects on IDO in vitro. Among them sixteen extracts showed more than 50% inhibition of IDO activity at the concentration of 30 ${mu}g/ml$. Especially, the extracts of Platycarya strobilacea, Quercus acutissima, Acer ginnala and Alnus japonica were most potent because their $IC_{50}$ value were 6.5, 8.1, 3.9 and 4.2 ${mu}g/ml$, respectively.