The radical scavenging activity of the stable derivatives, which are O-substituted at the C-2 position of ascorbic acid (AA), against 1, 1-diphenyl-2-picrylhydrazyl (DPPH) was evaluated in buffer under diffrent pH conditions, and compared with those of AA and α-tocopherol. AA was shown to have 50% radical scavenging ability (EC₅₀) at a concentration of 2.2×10^-5 M against 0.1 mM DPPH in 60% ethanol. Ascorbyl 6-palmitate, a lipophilic AA derivative which has a free endiol group and is therefore unstable, also showed potent radical scavenging activity with EC₅₀ of 2.9×10^-5 M. A typical lipophilic antioxidant, α-tocopherol gave a similar EC₅₀ value as that of AA. In contrast, ascorbyl 2, 6-dipalmitate, AA 2-phosphate and AA 2-sulfate exhibited negligible scavenging activity. On the other hand, 2-O-α-D-glucopyranosyl-L-ascorbic acid (AA-2G) and a series of 6-O-acyl-2-O-α-D-glucopyranosyl-L-ascorbic acids (6-Acyl-AA-2G) themselves exhibited the radical scavenging activity of EC₅₀: 6.1×10^-5 M and 4.4×10^-5-5.9×10^-5 M, respectively, although their activities were lower than that of AA. Among 6-Acyl-AA-2G derivatives, the EC₅₀ values tended to decrease with increasing length of their acyl carbon group. Increasing pH of the buffer resulted in decrease in the scavenging activity of all compounds tested as expected. We speculate that the difference in the radical scavenging activity of derivatives O-substituted at the C-2 position of AA may be ascribed to the linkage type of the substituent group to the endiol-lactone resonance system and the degree of dissociation of the C-3 proton.