Benign prostatic hyperplasia (BPH) is a common age-related urological disorder, and currently available treatments can cause adverse effects. HS1002 is a novel hybrid peptide derived from gonadotropin-releasing hormone (GnRH) and GV1001 that has demonstrated antitumor activity in prostate cancer. This study investigated the protective effects of HS1002 against testosterone propionate (TP)-induced BPH in castrated rats. BPH was induced by daily subcutaneous administration of TP (3 mg/kg) for 4 weeks. HS1002 (0.01, 0.1, or 1 mg/kg) was administered subcutaneously three times per week concurrently with TP for 4 weeks. At the end of the treatment period, the prostates were collected and evaluated using biochemical and histopathological analyses. TP administration significantly increased prostate weight and the prostatic index and induced marked glandular enlargement, confirming the successful establishment of BPH. HS1002 treatment attenuated these changes and ameliorated the TP-induced alterations in antioxidant enzyme activities and inflammatory markers. In addition, HS1002 significantly reduced 5α-reductase levels. These findings demonstrate that HS1002 suppresses TP-induced prostatic hyperplasia, potentially through the regulation of oxidative stress, inflammation, and androgen metabolism. Therefore, HS1002 may represent a promising therapeutic candidate for BPH; however, further studies are required to define its molecular mechanism and evaluate its clinical applicability.