We studied antioxidant activity and inhibitory effect of α-glucosidase from aqueous, ethanolic and methanolic fractions of Galla rhois. In FRAP and ORAC assay for measuring antioxidant activity, we confirmed that Galla rhois extracts had strong antioxidant activity and ethanolic and methanolic extracts were relatively stronger than aqueous extract. We used trolox as a positive control. In order to measure the inhibitory effect of α-glucosidase, we compared acarbose and Galla rhois extracts. As a result of α-glucosidase inhibitory assay, aqueous, ethanolic and methanolic extracts of Galla rhois showed high inhibitory activitity and ethanolic and methanolic extracts were relatively stronger than aqueous extract. The 50% inhibitory concentrations (IC50s) of acarbose, aqueous, ethanolic and methanolic fractions were 0.45 mM, 0.53 μg/mL, 0.415 μg/mL and 0.37 μg/mL, respectively. These results suggest that Galla rhois extracts can be a clinically useful anti-diabetic ingredient, indicating that it needs to be fractionated and isolated and should be further investigated.