BACKGROUND Regenerating liver after partial hepatectomy (PH) is susceptible to endotoxin. This study was conducted to investigate how morphological alteration by preoperative portal vein branch ligation (PVL) affects endotoxin-induced liver injury after PH. METHODS Male Sprague-Dawley rats were divided into a PVL group undergoing left PVL and into a non-PVL group receiving a sham operation. Seven days later, animals in both groups were subjected to PH (the left lateral, median and caudate lobes). Lipopolysaccharide (LPS) was intravenously administered to both groups 2 days after PH. RESULTS A significant increase in hepatocyte and sinusoidal endothelial cell proliferation assessed by Ki-67 immunostaining reached a peak at day 2 and 3 after PVL, respectively, in accordance with the changes in plasma interleukin-6 concentrations after PVL. The proliferation response of these cells after PH was observed in both groups, showing a significantly weaker response in the PVL group. The sinusoidal width after PH was significantly reduced in the non-PVL group when compared with that in the PVL group. LPS administration induced a marked elevation of plasma tumour necrosis factor-alpha levels in the non-PVL group compared with the PVL group. PVL before PH significantly attenuated endotoxin-induced functional and structural liver damage with greater hepatic polymorphonuclear leucocyte infiltration and microcirculatory derangement, resulting in an improvement in the 7-day survival rate. CONCLUSIONS Morphological alteration by PVL is of great advantage in preventing the development of endotoxin-induced liver injury in the regeneration process after PH.