OBJECTIVE: To investigate the efficacy of methanol-water extract of Inula helenium root against oxidative DNA damage.METHODS: Antioxidant properties of methanol-water extract of Inula helenium root were revealed by 2,2'-azinobis(3-ethylbenzothiazoline-6-suphonic acid) di-ammonium salt(ABTS), Folin-Ciocalteu and high-performance liquid chromatography(HPLC) methods. The effect against oxidative DNA base damage was determined analyzing oxidative DNA base damage products by GC-MS/MS.RESULTS: The methanol-water extract of Inula helenium root showed good antioxidant capacity[32.20 mg trolox equivalents(TE)/g dried weight(dw) by ABTS method, 54.53 mg TE/g dw by chromium reducing antioxidant capacity method] and total phenolic content [29.83 mg gallic acid equivalent(GAE)/g dw]. The chlorogenic acid, ferulic acid, rosmarinic acid and caffeic acid were determined in the extract by HPLC. The chlorogenic acid,ferulic acid and Inula helenium root extract were revealed to inhibit the oxidative DNA base damage by GC-MS/MS.CONCLUSION: The studies showed a crucial decrease in the amount of the DNA base damage products when antioxidants were used. The results showed that ferulic acid has better inhibition than chlorogenic acid for DNA oxidation. The methanol-water extract of Inula helenium root was determined to inhibit the oxidative DNA damage.