Drug-related hepatotoxicity has become a serious social issue nowadays. Acetaminophen (APAP) was widely used in clinical treatment, although commonly acknowledged that it is a general material that caused drug-related hepatotoxicity. In this study, triterpenoids (Trds) which are mainly composed of ursolic acid and oleanolic acid, were isolated and prepared from fruits of Sorbus pohuashanensis. Further, the effect of Trds against APAP-induced liver injury and the pharmacological mechanism were investigated. The results showed that Trds treatment significantly restrained the increase of serum aspartate transaminase (AST), alanine aminotransferase (ALT), tumor necrosis factor (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6), and hepatic malondialdehyde (MDA) levels, as well as evidently reversed the decrease of hepatic superoxide dismutase (SOD), glutathione (GSH) and catalase (CAT) levels induced by APAP. There are further evidences provided by liver histopathology which demonstrated Trds treatment observably inhibited hepatic tissues necrosis, hemorrhage and infiltration of inflammatory cell induced by APAP. According to the results of western-blot and RT-PCR, the over-expressions of inducible nitric oxide synthase (iNOS) and Cyclooxygenase-2 (COX-2) were inhibited by Trds. Moreover, Trds also effectively restrained APAP-induced phosphorylation of mitogen-activated protein kinase (MAPK) family signals such as p38, c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK). These results demonstrated the liver-protection effects that Trds exhibited were related to its property of anti-oxidantion and anti-inflammation.