Objective : Although chronic non-bacterial prostatitis is a common disease, it is very difficult to treat effectively. Lygodium japonicum has been traditionally used in treatment of urinary tract inflammation and voiding disturbance. In this study, we investigated the therapeutic effects and action mechanism of Lygodium japonicum in the rat model of non-bacterial prostatitis induced by castration and testosterone treatment. Methods : Five-month-old rats were treated with 17$eta$-estradiol after castration for induction of experimental non-bacterial prostatitis, which is similar to human chronic prostatitis in histopathological profiles. Lygodium japonicum and testosterone were administered as an experimental specimen and a positive control. respectively. The prostates were evaluated by histopathological parameters including the epithelial score and epithelio-stromal ratio for glandular damage. PCNA labeling index for cyto-proliferation and a TUNEL(deoxyuridine triphosphate biotin nick end-labeling) assay for cell apoptosis. Results : While prostates of control rats revealed severe acinar gland atrophy and stromal proliferation, the rats treated with Lygodium japonicum showed a diminished range of tissue damage. Epithelial score was improved in the Lygodium japonicum group over that of the control (P<0.05). The epithelio-stromal ratio was lower in the Lygodiutn japonicum group when compared to that of the control (P<0.05). Although there was no difference in PCNA and TUNEL positive cells of the glandular epithelia. we found an decreased number of PCNA positive cell and concurrent increase of TUNEL positive cells in the stroma of Lygodium japonicum treated rats (P<0.01). Conclusions : These findings suggest that Lygodium japonicum may protect the glandular epithelial cells and also inhibit stromal proliferation in association with suppression of cyto-proliferation and stimulation of apoptosis. We concluded that Lygodium japonicum could be a useful remedy agents for treating chronic non-bacterial prostatitis.