Objective: To investigate the antioxidant activity of Arenaria kansuensis extracts in vitro. Method: The air-dried and powderded herb of A. kansuensis was extracted over 2 hours with 10 times of 95% alcohol refluxing for 2 times and the combined alcohol extracts were concentrated under vacuum drying. The resultant residue was partitioned in petroleum ether

dichloromethane

ethyl acetate and n-butanol orderly. The four extracts were configured to the appropriate solution. The antioxidant activity of four extracts were analyzed by 1

1-diphenyl-2-pieryl-2-picrylhydrazyl (DPPH) radical scavenging

2

2-amino-di(3-ethyl-benzothiazoline sulphonic acid-6) ammonium salt (ABTS) radical scavenging

and ferric reducing antioxidant power (FRAP) assay. Result: The ethyl acetate and n-butanol extract of A. kansuensis showed stronger scavenging activity against DPPH ·

ABTS+ · and reducing antioxidant power of 2

4

6-tris (2-pyridyl) -s-triazine(TPTZ) than other extracts

but showed lower capacity than positive control of vitamin C. Conclusion: The scavenging effects showed a dose-response relationship at the selected concentration with the extracts of A. kansuensis. The ethyl acetate and n-butanol extract have the strongest free radical scavenging activity.