This study was performed to investigate antioxidant activities and glutathione S-transferase (GST) activity according to parts of the Acer mono and A. okamotoanum. Most extracts showed high scavenging activities on DPPH. Especially, the bark of A. okamotoanum showed higher activity as 98.4% than the control, BHA as 96.5%. A. mono and A. okamotoanum showed high ability on nitrite scavenging, but decreasing tendency according to decreasing of pH. On SOD-like test, the wood of A. okamotoanum showed highest activity as 35.4% at 1.0mg/ml concentration. Also, the extracts obtained high activity on GST test. Therefore, the water extracts from the bark of A. mono and A. okamotoanum have relatively good antioxidant activity and GST activity. Especially, the bark of A. okamotoanum showed the highest activity on all of extracts, could be the use of functional foods and biomaterials.