Hydroxyl radical (OH•) can cause severe damage to cells and tissues. However, its analysis is very difficult for its high reactivity and very short half-life. In this paper, a simple and highly sensitive method, capillary zone electrophoresis with amperometric detection (CZE-AD) was introduced indirectly to determine OH• by determining its reaction products with salicylic acid (SAL), 2, 3-dihydroxybenzoic acid (2, 3-DHBA) and 2, 5-dihydroxybenzoic acid (2, 5-DHBA). The optimum conditions of CZE-AD for the determination of 2, 3-DHBA and 2, 5-DHBA were explored. Under the optimum conditions, SAL, 2, 3-DHBA and 2, 5-DHBA could be perfectly separated within 15 min, and the linearity ranges of 2, 3-DHBA and 2, 5-DHBA were between 1.0×10−7 and 1.0×10−4 mol l−1. Their detection limits were as low as 2×10−8 mol l−1, which were much lower than that in CE-UV method. The method was also applied to study the free OH• scavenging activity of angelica polysaccharide. The experimental results showed that this CZE-AD method was very sensitive and practical in both the determination of free OH• and the evaluation offree OH• scavenging activities of antioxidants. 2003 Elsevier B. V. All rights reserved.