Objective The regulation of ornithine decarboxylase (ODC) gene expression and enzyme activity by corticosterone, the main glucocorticoid in rat, during rat liver regeneration induced by partial hepatectomy (PH) was evaluated. Methods Bilateral adrenalectomies (ADX) and sham-ADX were performed on ether-anesthetized rats 3 days before PH. Corticosterone in sesame oil was injected subcutaneously to adrenalectomied rats. ODC mRNA, ODC protein and enzyme activity were detected by RT-PCR, Western blotting and high performance liquid chromatography (HPLC), respectively. Results The ODC mRNA levels, protein accumulation and enzyme activity were lower in the intact liver compared to the regenerating liver. After PH, mRNA levels were remarkably enhanced in all groups (EM>n/EM>=6 in each group) and peaked at 5 hours postPH. Till 7 hours, the contents in all groups from high to low were ADX group,control group (Sham-ADX group), ADX treated with 10mg/kg and 40mg/kg body weight corticosterone group, respectively. ODC protein accumulation in ADX rats was higher than that in control rats (EM>n/EM>=13, the same below), but it decreased in corticosteronetreated (10mg/kg) rats until 24 hours post-PH, with a strong decline seen in 40mg/kg corticosteronetreated rats. ODC activity was rapidly promoted, and the highest levels were observed at 6 hours after PH in all groups (EM>n/EM>=6 in each group). After corticosterone treatment, the activities declined significantly at 6 hours post-PH, with the lowest value found in the 40mg/kg group. Conclusion Corticosterone treatment results in dose-dependent decreases in ODC mRNA and enzyme protein both in the intact liver and the regenerating liver. The change in ODC activity is partia