Voiding dysfunction is the primary clinical manifestation of chronic prostatitis (CP), which is a common urological disease. The present study investigated whether prostate fibrosis was associated with urinary dysfunction in CP and if resveratrol improved urinary dysfunction, and the underlying molecular mechanism. A rat model of CP was established via subcutaneous injections of the pertussis‑diphtheria‑tetanus vaccine, which was followed by treatment with resveratrol. Bladder pressure and volume tests were performed to investigate the effect of resveratrol on urinary dysfunction in CP rats. Western blotting and immunohistochemical staining examined the expression levels of tryptase, chymase, transforming growth factor (TGF)‑β, Wnt and α‑smooth muscle actin (α‑SMA). The results demonstrated that the maximum capacity of the bladder, residual urine volume and maximum voiding pressure were increased significantly in the CP group compared with the control group. Mast cell (MC) activation, the activity of TGF‑β/Wnt/β‑catenin pathways, and the expression levels of tryptase and α‑SMA in the CP group were increased significantly compared with the control group. Resveratrol treatment significantly reversed these factors. Therefore, the results indicate that MC infiltration may induce prostate fibrosis, which exhibits a close association with urinary dysfunction in CP. Resveratrol may improve fibrosis via the suppression of MC activation and TGF‑β/Wnt/β‑catenin pathway activities.