This study was designed to investigate the effectiveness of protamine sulfate as an apelin receptor blocker on cholestatic liver fibrosis persuaded by common bile duct ligation (BDL) in experimental rats and to examine some of the related mechanisms. Three groups of adult male Wistar rats were included: control (sham-operated), BDL, and BDL + protamine sulfate groups. All groups were examined after 4 weeks for serum apelin, total bilirubin, aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), hepatic interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-), superoxide dismutase (SOD), glutathione peroxidase (GPx), malondialdehyde (MDA), transforming growth factor- (TGF-), and hydroxyproline content, and for extracted[PF1][H2] liver histopathological studies. BDL significantly increased serum apelin, total bilirubin, AST, ALT, ALP, hepatic IL-6, TNF-, MDA, TGF- and hydroxyproline content, but it significantly reduced serum albumin level and hepatic GPx and SOD activities. Serum level of apelin significantly revealed positive correlations with TNF-, MDA, TGF-, and hydroxyproline content. On the other hand, protamine sulfate significantly attenuated these changes, with no effect on either serum apelin or bilirubin levels, in the treated group. It also improved the hepatic histopathological changes. Protamine sulfate, maybe through its apelin receptor blockade, ameliorated cholestatic liver injury, inflammation, and fibrosis induced by BDL.