Objective To examine the incidence and pathological characteristics of spontaneous liver bile duct hyperplasia in aging rats. Methods Rats were divided into three groups: Group 1, 30 imported Sprague Dawley (SD) male rats and 30 imported SD females; Group 2, 60 domestic SD males and 60 domestic SD females; and Group 3, 60 domestic Wistar males and 60 domestic Wistar females. The animals were euthanized after feeding for 104 weeks. The livers were collected for conventional histopathological and immunohistochemical analyses. Results Bile duct hyperplasia was observed in all groups, with an overall incidence rate of 32. 33%. However, the incidence rate of bile duct hyperplasia in domestic SD rats was higher than that in the imported SD rats (26. 67% vs 1. 67%, respectively), the incidence rate was higher in domestic Wistar rats than that in domestic SD rats (53. 33% vs 26. 67%, respectively), and the incidence rate was higher in the male rats than that in the female rats (20% vs 12. 33%, respectively). Multiple morphological bile duct hyperplasia findings with fibrosis were seen by pathological examination. We defined three hyperplasia grades to evaluate the pathological lesions. The incidence rate of lesions in grade I and grade II was 84. 5%, while the incidence of lesions in grade III was 15. 5%. Hyperplasia of oval cells was observed in cases with bile duct hyperplasia, with differentiation to bile duct epithelium. Conclusions The incidence rate of liver bile duct hyperplasia in aging rats varies by species and sex. These data provide a reference for studies on liver bile duct hyperplasia in ageing animals and humans.