We investigated the effects of an extract of Radix Rosa laevigata (R. R. laevigata) on Propionibacterium acnes (P. acnes) and lipopolysaccharide (LPS)-induced acute liver injury. The plasma alanine aminotransferase (ALT) activity was significantly elevated by an intravenous injection of heat-killed P. acnes at a dose of 0.4 mg/mouse and then with LPS at 0.1 microg/mouse after 5 d. However, the elevated ALT activity was significantly reduced by the administered of R. R. laevigata (125 and 500 mg/kg/d) for 7 d before the LPS injection. In addition, the extract treatment reduced the number of liver mononuclear cells (MNCs), and malondialdehyde (MDA) and nitric oxide (NO) contents, but improved the liver oxygen radical absorbance capacity (ORAC) and mitochondrial membrane potential. Moreover, the chemical profile of R. R. laevigata was performed by high-performance liquid chromatography (HPLC) and the main peaks were identified as a series of polyphenol compounds which had been confirmed as the significantly active components by their anti-oxidative and NO inhibitory effects. These results suggest that the extract of R. R. laevigata offered good efficacy for preventing liver injury.