A micro-assay was developed and validated, using a microplate reader in 96-well format, C(11)-BODIPY(581/591) as fluorescent probe and AIBN as ROO() generator. The structure-activity relationship was established for 15 carotenoid standards, indicating that the opening of the β-ionone ring and the increase of chromophore extension in the carotenoid structure were the major factors leading to the increase of ROO() scavenging capacity. The values for ROO() scavenging capacity were calculated using α-tocopherol as reference compound. Among the studied carotenoids, all-trans-lycopene was the most efficient ROO() scavenger (8.67±0.74) followed by all-trans-astaxanthin (6.50±0.62). All the carotenoids showed to be more effective ROO() scavengers than α-tocopherol and some hydrophilic compounds. Finally, the method was successfully applied to assay the ROO() scavenging capacity of carotenoid extracts from two Amazonian fruits, peach palm (7.83±0.21) and mamey (6.90±0.44).1352103-11