Abbreviations & Acronyms BC = bladder capacity BP = base pressure BPS = bladder pain syndrome BW-A = bodyweight after instillation BW-B = bodyweight before instillation CMG = cystometry CYP = cyclophosphamide GAG = glycosaminoglycan GAPDH = glyceraldehydes-3-phosphate dehydrogenase HA = hyaluronic acid HAase = hyaluronidase HHAase = high-dose hyaluronidase IC = interstitial cystitis ICAM-1 = intercellular adhesion molecule-1 ICI = intercontraction intervals IL = interleukin LHAase = low-dose hyaluronidase mRNA = messenger ribonucleic acid PP = peak pressure PS = protamine sulfate RNA = ribonucleic acid RT-PCR = reverse transcription polymerase chain reaction RV = residual volume TNF = tumor necrosis factor UPIII = uroplakin III Zo-1 = zonula occludens-1 Objectives: To determine whether a potential rat model of bladder pain syndrome could be developed through long-term intermittent intravesical hyaluronidase. Methods: A total of 64 female Sprague-Dawley rats were divided into a control group, a low-dose hyaluronidase (1 mg/mL) group, a high-dose hyaluronidase (4 mg/mL) group and a hyaluronic acid-treated group. Hyaluronidase was given intravesically three times a week for 1 month. Hyaluronic acid (0.5 mL, 0.8 mg/mL) was introduced intravesically to hyaluronidasetreated rats' bladders. Histological changes, cystometry, nociceptive behaviors, and messenger ribonucleic acid levels of inflammatory factors were evaluated and compared between groups. Results: All hyaluronidase-treated rats showed chronic inflammation and fibrosis, increased and activated mast cells, thinned bladder epithelium with abnormal expressions of uroplakin III and zonula occluden-1, and increased levels of interleukin-6 and intercellular adhesion molecule-1 messenger ribonucleic acid. However, the inflammatory score and levels of interleukin-6 and intercellular adhesion molecule-1 were more significant in the high-dose hyaluronidase group than in the low-dose hyaluronidase group (P < 0.01). Furthermore, hyaluronidase-treated rats showed markedly decreased intercontraction intervals, bladder capacity and increased sensitivity to pain compared with controls (P < 0.01). Hyaluronic acid treatment significantly decreased the inflammatory level, number of mast cells, sensitivity to pain, levels of interleukin-6 and intercellular adhesion molecule-1, and increased intercontraction intervals and bladder capacity (P < 0.01). Conclusions: Long-term intermittent intravesical hyaluronidase could develop a severe chronic cystitis with diffused fibrosis accompanied by altered histology and bladder function. This chronic cystitis rat model can resemble the clinical and histopathological features of human bladder pain syndrome, and might be a potential valuable model for investigation of this troublesome disease.