Background: Serine/threonine kinase 1 (PIM1) plays a crucial role in cell growth, differentiation, and apoptosis. However, its role in the pathogenesis of concanavalin A (ConA)-induced acute hepatitis is not well understood. PIM1 kinase inhibitor can reduce the expression of PIM1. This study aims to investigate the effects of PIM1 kinase inhibitor and its protective mechanism in ConA-induced acute hepatitis., Methods: C57/BL six mice were injected with ConA (20, 15, and 12 mg/kg) to induce acute hepatitis, and PIM1 kinase inhibitor SMI-4a (60 mg/kg) was administered orally 24 h before ConA injection. The survival rate of the mice was observed after ConA injection. The levels of serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were measured. Serum inflammatory factors were detected by enzyme-linked immunosorbent assay (ELISA). Hematoxylin-eosin (HE) staining was performed on liver tissue collected at different time points. The major cytokines expression in liver tissue was detected by quantitative real-time polymerase chain reaction (qRT-PCR). The number of macrophages, T-cell and neutrophils in liver tissue were detected by flow cytometry (FCM). PIM1 in liver tissue was detected by western blot (WB) and qRT-PCR. SMI-4a (80 µM) was pretreated for 24 h and ConA (400 µg/mL) was stimulated for 12 h in RAW264.7 cell model. Phosphorylated p65 (p-p65) and cleaved caspase-3 (c-caspase-3) in liver tissue and macrophages were detected by WB., Results: Different concentrations of ConA caused different acute hepatitis mortality, 12 mg/kg concentration within 24 h of the mortality showed a gradient increase. The levels of AST and ALT increased significantly at 12 h after ConA injection. PIM1 expression was upregulated at 12 h. SMI-4a can suppress the PIM1 expression. SMI-4a suppressed cytokines production, AST, and ALT in ConA-treated serum. SMI-4a suppressed the major cytokines in liver tissue. Tests in liver tissue showed that SMI-4a reduced the number of T cells, neutrophils, and macrophages. SMI-4a inhibited the inflammatory response by downregulating the expression of p-p65. Meanwhile, apoptosis was decreased by decreasing the expression of c-caspase-3., Conclusions: In conclusion, the protective effect of SMI-4a against acute hepatitis is by reducing the inflammatory response and apoptosis. These findings suggest that SMI-4a may have therapeutic potential in the treatment of autoimmune hepatitis., Competing Interests: Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tgh.amegroups.com/article/view/10.21037/tgh-23-93/coif). The authors have no conflicts of interest to declare., (2024 Translational Gastroenterology and Hepatology. All rights reserved.)