Objective: To study the antioxidant activity of essential oils of Ageratum conyzoides. Method: The essential oils of A. conyzoides were preparated into different doses (0.4

0.8

1.2

1.6

2.0 g·L-1) with 95% ethanol. And the antioxidant activities were studied using DPPH assay

ABTS+·assay and reducing power assay. Result: The reducing power of iron ion and the scavenging activities of ABTS+·radical and DPPH radical were enhanced while the concentration of oil was increased(in the sequence of 2.0 g·L-1>1.6 g·L-1>1.2 g·L-1>0.8 g·L-1>0.4 g·L-1). The ABTS+·radical scavenging rate reached to 64.63%

but the maximal DPPH radical scavenging rate just reached to 19.61%. Conclusion: The essential oils of A. conyzoides showed good activities on both scavenging ABTS+·radical and reducing power

but low activity on scavenging DPPH radical. All antioxidant activity showed a concentration-effect relationship. The essential oils can be employed as natural antioxidants and health care products.