Objective : The etiology of chronic prostatitis is likely multifactorial, resulting from either a cascade of events after an initiating factor or from a variety of etiologic mechanisms. There is substantiating evidence to support the role of the inflammatory responses in its pathogenesis, and the clinical value in the evaluation of therapeutic efficacy. Forsythiae Frucus has been traditionally used in treatment of inflammatory diseases, including of prostatitis and urinary tract inflammation. In this study, we investigated the effects of Forsythiae Frucus on inflammatory cytokines and cyto-pathological alternation in the rat model of chronic non-bacterial prostatitis induced by castration and $17{eta}$-estradiol treatment. Methods : Two-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. Forsythiae Frucus as an experimental specimen, and testosterone as a positive control, were administered orally. The prostates were evaluated by histopathologlcal parameters including the epithelial score and epithelio-stromal ratio for glandular damage. and the expression of inflammatory cytokine genes including interleukin (IL)-$1{eta}$, IL-5, IL-12, tumor necrosis factor (TNF)-$alpha$. eotaxin, inducible nitric oxide synthase (iNOS) and cyclooxygenase-2(cox-2). Results : While prostates of control rats revealed severe acinar gland atrophy and stromal proliferation. the rats treated with Forsythiae Frucus showed a diminished range of tissue damage. Epithelial score was improved in the Forsythiae Frucus group over that of the control (P<0.05). The epithelia-stromal ratio was lower in the Forsythiae Frucus group when compared to that of the control (P<0.05). In the reverse transcription-polymerase chain reaction (RT-PCR) of inflammatory cytosine genes. Forsythiae Frucus inhibited the expression of IL-$1{eta}$, TNF-$alpha$, iNOS, cox-2 genes, while it modulated the expression of IL-5, which is an anti-inflammatory cytokine. Conclusions : These findings suggest that Forsythiae Frucus may protect the glandular epithelial cells and also inhibit stromal proliferation in association with the immune modulation including the suppression of inflammatory cytokines and increase of anti-inflammatory cytokines. From theses results. we suggest that Forsythiae Frucus could be a useful remedy agents for treating chronic non-bacterial prostatitis.