The aim of the present study was to determine whether the intensity of bronchiolar epithelial cell injury is ameliorated by transbronchial human IL-10 (hIL-10) gene transfer in a rat model of lung allograft rejection. The left lung was extracted from a donor Brown Norway rat and transbronchially instilled with encoding hIL-10 (IL-10 group) or β-galactosidase (control group). The lung graft was then transplanted into a Lewis rat and harvested on day 6 after transplantation. The allografts were histologically examined and all bronchioles in the slides were assigned one of three grades according to the intensity of epithelial cell loss. The distribution of the grades was significantly different between the two groups, and the epithelial cell injury was significantly improved in the IL-10 group. The present study demonstrated the effect of transbronchial hIL-10 gene transfer on ameliorating bronchiolar epithelial cell injury in a rat model of lung allograft rejection.