In this study, we evaluated the effects of HBO therapy on oxidant and antioxidant status, and some histopathological parameters after partial hepatectomy in rats. There were three main experimental groups. The first group was sham (S) group (n=12), the second group was partial hepatectornized (PH) group (n=24) and the third group was after partial hepatectomy HBO-treated group (PH+HBO) (n=24). The HBO therapy was started the same day as partial hepatectomy for the PH+HBO group. Three subgroups (n=8) were assigned from the PH and HBO groups. The first, the second and the third subgroups were selected randomly, separated from the main groups and killed 2 days, 4 days and 7 days after partial hepatectomy respectively. Randomized selection from the main experimental groups and killing of the animals were done on the same day. Malondialdehyde (MDA), glutathione (GSH), nitric oxide (NO), mitotic index (MI), proliferating cell nuclear antigen (PCNA) levels and mean of cells with double nuclei were assessed. In the PH+HBO group, MDA and NO levels were decreased and MI, PCNA, GSH levels were increased significantly compared to the PH group. HBO therapy could activate antioxidant response and reduce oxidant activity after partial hepatectomy.