To analyse the antioxidant and antidiabetic activities of Rehmannia glutinosa tuberous roots, extracts with nine different solvents were investigated. Antioxidant activity was measured with two methods, 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging and reducing power. Each extract exhibited a dose-dependent free radical scavenging action against DPPH and a reducing power, but diverse antioxidant activities. To determine the antidiabetic activity, we measured the alpha-glucosidase inhibitory capacity of each extract. We found that 10 mu g/ml of 60% MeOH or 80% of MeOH extract inhibited more than 90% of alpha-glucosidase activity, and this inhibitory activity was not mediated by catalpol, a major iridoid constituent of R. glutinosa tuberous roots. Overall, the data suggested that the tuberous roots of R. glutinosa have potential as natural antioxidants and antidiabetics.