The purpose of this study was to evaluate the protective effects of α-mangostin against acetaminophen (APAP)-induced acute liver injury and discover its potential mechanisms in mice. Mice were continuously treated with α-mangostin (12.5 and 25 mg/kg) by intragastric administration once daily for 6 days, and injected intraperitoneally with APAP (300 mg/kg) after 1 h of α-mangostin administration on the last day. After APAP exposure for 24 h, the liver and serum were gathered to evaluate the hepatotoxicity. The results showed that α-mangostin effectively decreased the serum levels of alanine aminotransferase, aspartate transaminase, tumor necrosis factor (TNF-α), interleukin-1β and 6 (IL-1β, IL-6), and hepatic malondialdehyde level; and recovered hepatic glutathione (GSH), superoxide dismutase and catalase activities. Liver histopathological observation provided further evidence that α-mangostin pretreatment significantly inhibited APAP-induced hepatocellular necrosis, infiltration of inflammatory cell and hyperemia. According to the analysis of western-blot and RT-PCR detection, α-mangostin pretreatment validly inhibited the phosphorylation of ERK, JNK and p38 MAPK induced by APAP, which was consistent with the changes of TNF-α, IL-6 and IL-1β levels; the phosphorylation of IκBα and the translocation of NF-κBp65 were also attenuated by α-mangostin. These results provided a new mechanism for the protective effects of α-mangostin against APAP-induced acute liver injury. α-Mangostin significantly restrainted the oxidative stress induced by APAP. Moreover, the anti-inflammatory property of α-mangostin, which is mediated by the NF-κB and MAPK signaling pathways, also contributed to its hepatoprotective effect. Taken together, we believed that α-mangostin might be a potential material for drug development against drug-related hepatotoxicity.