Abstract: Objective To investigate whether phenotypic modulation of bladder smooth muscle occurs in diabetic rats. Methods Thirty-two male SD rats were randomly assigned into diabetic group and control group. Diabetic rat models were established by a single intraperitoneal injection of streptozotocin (60 mg/kg). Nine weeks later, the bladder tissues of the rats were examined for structural changes using HE and Masson’s trichrome staining , and the expressions of myocardin, α-SMA, and SMMHC in bladder smooth muscles were detected with RT-PCR and Western blotting. Results Compared with the control group, the diabetic rats showed obvious polydipsia and polyuria with significantly increased collagenous fibers and lowered expressions of myocardin, α-SMA, and SMMHC in the bladder tissue (P<0.05). Conclusions In rats at 9 weeks after diabetic model establishment, phenotypic transition of the bladder smooth muscles occurs to cause bladder contractile dysfunction, which may play an important role in the pathology of diabetic bladder dysfunction.