To determine the therapeutic effects of the Zhuangyao Jianshen pill (, ZYJSP) against benign prostatic hyperplasia (BPH) and investigate the underlying mechanism. Forty-eight male Sprague-Dawley rats were randomly divided into six groups: Control group, BPH model group, finasteride-treated group, ZYJSP low, medium and high dose groups. Except for the control group, 40 rats were castrated and injected with testosterone propionate (TP) for 28 consecutive day to induce BPH. Meanwhile, the corresponding drugs were administered by gavage. The prostate wet weight, prostate index (PI), and the histopathological changes in the prostate were measured as the basis for examining the efficacy of ZYJSP against BPH. Levels of the serum sex hormones, oxidative stress markers, inflammatory markers, renal function markers, growth factors, and Cyclin D1 expression in prostate were measured to characterize the therapeutic mechanism of ZYJSP against BPH. ZYJSP administration significantly reduced prostate wet weight and PI and ameliorated histological changes of the prostate in TP-treated castrated rats. TP markedly increased the levels of creatinine, blood urea nitrogen and growth factors in the serum as well as the expression of the Cyclin D1 in the prostate. Most of these markers were significantly decreased by ZYJSP. ZYJSP significantly restored the dysregulation of testosterone, estradiol, and dihydrotestosterone caused by TP. Furthermore, ZYJSP relieved TP-induced prostate injury and exhibited both anti-inflammatory and anti-oxidant activity by decreasing interleukin-6, interleukin-8, and malondialdehyde levels and increasing the activity of superoxide dismutase in the serum. These findings indicate that ZYJSP can effectively ameliorate BPH induced by TP in castrated rats, and the underlying mechanism might be related to regulating sex hormone balance, reducing oxidative stress, and inhibiting the inflammatory response.