Prostate cancer (PCa) is the most common male cancer. Most patients treated with androgen deprivation therapy progress to castration-resistant PCa. To overcome the limitations of this treatment, there is an urgent need to identify more effective treatment targets. High mobility group box 1 protein (HMGB1) is known to be associated with progression, metastasis, and poor prognosis of several solid tumors; however, its role in PCa remains unclear. Thus, we aimed to evaluate the clinical significance and biological roles and mechanism of HMGB1 in PCa. We showed that increased expression of HMGB1 correlated with increased risk of aggressive PCa, and high expression of HMGB1 was associated with poor biochemical recurrence-free survival in a Korean cohort. Additionally, the inhibition of HMGB1 expression significantly reduced cell proliferation, invasive capacity, and NF-κB signaling in vitro. Our results indicated that HMGB1 is a critical factor in the development and progression of PCa. Moreover, we found that HMGB1 directly interacts with TNFR1, and TNFR1 overexpression in HMGB1 knockdown cells reversed the effects of HMGB1 knockdown. Importantly, our results suggest that HMGB1 binding to TNFR1 promotes tumor progression by activating the NF-κB signaling pathway in PCa; therefore, the HMGB1/TNFR1/NF-κB signaling pathway could serve as a novel therapeutic target for improving PCa therapy.