Urinary bladder dysfunction caused by the alteration of detrusor smooth muscle (DSM) is one of the complications of diabetes. It is well established that smooth muscle contractility is regulated by an elevation of cytosolic Ca²⁺ via myosin light chain (MLC) phosphorylation. However, recent studies have shown the modulation of MLC phosphorylation without a rise in Ca²⁺ in smooth muscle, and two key molecules (Rho-kinase and CPI-17) are involved in the regulation of calcium sensitization. This study investigates the effect of diabetes on DSM calcium sensitization. Diabetes was induced by alloxan in New Zealand White rabbits, and age-match rabbits given 5% sucrose in the drinking water served as control for diuresis. 2D gel electrophoresis showed that basal MLC phosphorylation level was significantly higher in diabetic animals than normal or diuretic controls, and Rho-kinase specific inhibitor, Y-27632, decreased MLC phosphorylation level. Adding Y-27632 to bethenachol-precontracted DSM strips can induce muscle relaxation, but it occurred much more slowly in diabetic samples compared with controls. RT-PCR, Western-blot and immuno-histochemistry revealed the over-expression of Rho-kinase and CPI-17 at both mRNA and protein levels in response to diabetes. In conclusion, our results demonstrate that Rho-kinase contributes to DSM MLC phosphorylation and there is a higher basal MLC phosphorylation level in diabetic DSM. Our results also suggest that this high basal MLC phosphorylation may be due to the up-regulation of Rho-kinase and CPI-17. Thus, Rho-kinase and CPI-17- mediated Ca²⁺ sensitization might play a role in diabetes-induced alteration of the detrusor contractility and bladder dysfunction.