OBJECTIVE： Compare the contents of free ellagic acid and total ellagic acid in fruits， roots and levels of Rosa roxburghii， and to evaluate the in vitro anti-oxidant activity of ethanol extract of three medicinal parts of R. roxburghii. METHODS： Free ellagic acid and total ellagic acid were obtained from different medicinal parts of R. roxburghii by ultrasonic extraction and acid hydrolysis， respectively. The contents of them were determined by UPLC. Using half-clearance value （IC50） as anti-oxidant evaluation index， free radical scavenging test of 1，1-diphenyl-2-trinitrophenylhydrazine （DPPH） and 2，2′ -binitro-bis（3-ethylbenzothiazoline-6-sulfonic acid） （ABTS） were conducted for ethanol extract of different medicinal part， using vitamin C （VC） as positive control. RESULTS： There were significant differences in the content of free ellagic acid and total ellagic acid in different medicinal parts of R. roxburghii. The content level of free ellagic acid was in descending order： R. roxburghii leaves （38.49 mg/g）＞R. roxburghii fruits （20.59 mg/g）＞R. roxburghii roots （11.35 mg/g）； the content level of total ellagic acid was in descending order： R. roxburghii leaves （197.08 mg/g） ＞ R. roxburghii fruits （49.36 mg/g） ＞ R. roxburghii roots （21.86 mg/g）. The contents of total ellagic acid in the fruits and roots of R. roxburghii were twice as much as that of free ellagic acid in corresponding parts； the contnets of total ellagic acid in the leaves of R. roxburghii were five times higher than that of free ellagic acid in corresponding parts. In the DPPH free radical scavenging test and ABTS free radical scavenging test， the order of antioxidant activity was VC ＞ R. roxburghii leaves＞R. roxburghii fruits＞R. roxburghii roots. There was no statistical significance in the effects of R. roxburghii leaves [IC50 to DPPH free radical and ABTS free radical were （4.57±0.70）、（115.99±2.21） μg/mL] and R. roxburghii fruits [IC50 to DPPH free radical and ABTS free radical were （5.12±0.24）、（127.61±3.31）    μg/mL]， compared with the effects of VC [IC50 to DPPH free radical and ABTS free radical were （4.47±0.38）、（121.42±2.65）      μg/mL] （P＞0.05）. CONCLUSIONS： Among fruits， roots and leaves of R. roxburghii， the content of free （total） ellagic acid is the highest in the R. roxburghii leaves and in vitro anti-oxidant activity of its ethanol extract is the strongest.