Aims: To demonstrate changes in the number of suburothelial myofibroblasts in the rat bladder due to chronic urinary retention (CUR). Methods: Bladder specimens were obtained from 12-week-old Wistar female rats that were divided into two groups: a CUR group and a sham-operated group. In the CUR rats, the urethra was intubated with a polyethylene catheter, and a double 4-0 silk ligature was placed around the proximal urethra, after which the catheter was removed. After 8 weeks, the cystometric findings and immunohistochemical staining of the suburothelial myofibroblasts were compared between the groups. Results: The bladder weight of the control rats was 0.20 ± 0.01 g and that of CUR rats 1.6 ± 0.4 g. The bladder capacity of the control rats was 0.5 ± 0.3 ml and that of the CUR rats 12.9 ± 3.1 ml. The number of suburothelial myofibroblasts of the control rats was 417 ± 123 and that of the CUR rats 44 ± 42. The number of suburothelial myofibroblasts in the CUR rats was significantly less than that observed in the sham-operated rats (p < 0.01). Conclusions: In this study, we demonstrated that mechanical stress over a long period on the bladder wall can decrease the number of suburothelial myofibroblasts. The reduced expression of suburothelial myofibroblasts may be related to prolongation of the micturition interval by CUR.