Ketamine abusers have greatly increased in number worldwide during recent years. The consumption of ketamine has increased, as have the number of published accounts of devastating urological sequelae. However, the mechanism of ketamine-associated urinary tract dysfunction remains unclear. This study was to evaluate the ketamine dose-dependency of ketamine-induced cystitis (KC) in a rat model. A total of 42 Sprague-Dawley rats (female, 10-week-old) were used. Each of the 7 KC rat models were induced by 1, 5, 10, 25 and 50 mg/kg ketamine intravenous injection for two weeks. For the sham group (n = 7), a phosphate-buffered saline (PBS) vehicle was used rather than ketamine hydrochloride. The cystometric parameters, histological examinations, staining for Masson's trichome, cytokeratin, toluidine blue and quantitative PCR were measured at two weeks following the intervention. The voiding interval gradually decreased depending upon the ketamine dose of 1, 5, 10, 25, or 50 mg/kg, respectively, and was decreased compared with Sham. Bladder capacity was decreased as ketamine dose increased. In particular, the increase of fibrosis and submucosal apoptosis were found according to the increase of the ketamine dose. The bladder apoptosis in the KC rat model makes the fibrotic bladder change, and led us to hypothesize that fibrosis could contribute to the lower urinary-tract symptoms. We suggest that according to the pathophysiology evidence, fibrosis induced by apoptosis plays a key role in KC.