The abilities of scavenging reactive oxygen species (ROS, O^{- 2}, OH·, H₂O₂ ) of the extracts from the seeds of Brassica campestris Linn. were studied by chemical luminescence. The results showed that the extracts by hot extraction and cold-maceration extraction both had scavenging effect on ROS, their IC₅₀ to O^{- 2}, OH· and H₂O₂ were 0.033 3, 0.030 8, 6.81×10^-4 and 0.051 1, 0.025 3, 9.40×10^-4 mg·mL^-1 respectively. The antioxidant A separated from the extracts had the significant scavenging effect of O^{- 2}, OH·, H₂O_2, IC₅₀ were 0.003 14, 0.001 62 and 5.96×10 ^-6 mg·mL ^-1 respectively, obviously stronger than tea-polyphenols.