This study determined whether or not benign prostatic hyperplasia (BPH) induced by a high-fat diet (HFD) is involved in inflammatory responses, apoptosis, and the signal transducer and activator of transcription (STAT3)/nuclear factor-kappa B (NF-κB)- and nuclear factor erythroid 2-related factor 2 (Nrf2)-mediated oxidative stress pathways. Forty rats were divided into four groups: control; HFD; testosterone; and HFD+testosterone. Hematoxylin and eosin (HE) staining was used to assess histologic changes. An enzyme-linked immunosorbent assay and Western blot analysis were used to detect levels of related proteins. Compared with the control group, the prostate levels of cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), malondialdehyde (MDA), transforming growth factor-β1 (TGF-β1), and monocyte chemotactic protein-1 (MCP-1) were significantly increased, while the levels of glutathione peroxidase (GSH-Px), glutathione reductase (GR), glutathione (GSH), and superoxide dismutase (SOD) were decreased. The TNF-κB, Bcl-2, and caspase-3 levels were increased, while the Bax level was markedly decreased. The cytoplasmic expression of STAT3 and NF-κB was increased, while the nuclear expression of Nrf2 was markedly decreased compared with the control group. In summary, our results demonstrated that a long-term HFD might cause changes in inflammatory responses, apoptosis, and oxidative stress, thus contributing to prostatic hyperplasia. The underlying mechanisms might be related to the STAT3/NF-κB- and Nrf2-mediated oxidative stress pathway.