Objective To determine the effect of stem cell factor (SCF) on the number of interstitial cells of Cajal (ICCs) and the contraction of detrusor in the rats with underactive bladder. Methods A total of 54 SD rats were randomly divided into 3 groups: control group, detrusor underactivity group (DU, inflicted with bladder outlet obstruction), and DU+SCF group [intra-peritoneal injection of 0.2 μg/(kg·d) SCF], with 18 animals in each group. After the rats were sacrificed in 2 weeks later, their blood and bladder samples were harvested. The number of ICCs was analyzed by immunohistochemical and immunofluorescent staining. The serum SCF levels were detected by ELISA. The expression levels of c-kit and SCF in the detrusor tissues were detected by RT-PCR and Western blotting. Change of detrusor spontaneous contraction was tested with detrusor strips in vitro. Results The number of ICCs was decreased significantly, the serum SCF level was also reduced significantly, so were the expression of c-kit and SCF at mRNA and protein levels, and the contraction of detrusor was decreased significantly in the DU group compared to the control group (all P<0.05). However, exogenous SCF resulted in the increase of ICCs number, enhancement of c-kit and SCF expression levels, and significant improvement of the contraction amplitude and frequence of detrusor (all P<0.05). Conclusion Exogenous SCF improves the number of ICCs and the contraction of detrusor in DU rats.