Drug-induced liver injury and herbal preparations containing pyrrolizidine alkaloid (PA) have gained global attention. The purpose of this research was to investigate the effects and mechanisms of Alismatis Rhizoma, a traditional Chinese medicine, to protect against acute liver injury in mice induced by senecionine (SEN), a representative toxic PA compound. All experiments were approved by the Animal Research Committee of Shanghai University of Traditional Chinese Medicine. Animal welfare and the animal experimental protocols were strictly consistent with related ethics regulations of Shanghai University of Traditional Chinese Medicine. Acute liver injury was induced by a single intragastric administration of SEN (50 mg·kg-1). Mice in the protection groups received intragastric administration of Alismatis Rhizoma water extract (WE, 18 g·kg-1 per day) or ethanol extract (EE, 18 g·kg-1 per day) 5 days before SEN treatment. The results show that Alismatis Rhizoma extracts can significantly attenuate acute liver injury in mice. Mice in the protection groups showed decreased serum activities of alanine aminotransferase and aspartate aminotransferase, as well as decreased total bile acids. In addition, the infiltration of inflammatory cells, sinusoidal hemorrhage, and hepatic necrosis in SEN-treatment mice was clearly attenuated in the protection groups. Interestingly, EE showed a better effect than WE. The content of principal bile acids in serum and the mRNA and protein expression of key factors related to bile acid metabolism were also measured. Alismatis Rhizoma up-regulated the bile acid transporters and drug metabolism enzymes, consistent with the observed bile acid homeostasis and alleviation of SEN-induced injury to hepatocytes. The present study points to the possibility of utilizing Alismatis Rhizoma for protection against liver injury caused by drugs and preparations containing PA.