Background: Intradetrusor botulinum toxin A injection is recommended for the treatment of refractory detrusor overactivity (DO) in patients with neurogenic bladder, however, whether it could inhibit neurogenic bladder fibrosis is uncertain. This study aimed to investigate the effect of botulinum toxin A on neurogenic bladder fibrosis and the underlying mechanism. Methods: Forty eight Female Wistar rats were evenly randomized into 4 groups: Sham, T10 transection, Early and Late groups. The last three groups were subjected to T10 spinal cord transection, while the Sham group was treated with sham surgery. 0.9% saline was injected into the detrusor in the Sham and T10 transection groups simultaneously with the surgery, while 2 U/rat botulinum toxin A was injected into the detrusor simultaneously with the surgery in the Early group and 4 weeks following the surgery in the Late group. Body/bladder weight, cystometric parameters, bladder Hematoxylin-eosin staining were used to evaluate the bladder fibrosis. Western blot and quantitative Real-time PCR were used to evaluate the expression of bladder transforming growth factor beta 1. Results: Compared with the T10 transection group, the bladder/body weight was decreased significantly in the Early and Late groups (P<0.05), along with the significant inhibition of non-voiding contraction (NVC) frequency and amplitude (P<0.05), and the significant increase of bladder volume (P<0.05). The detrusor connective tissue percentage (P<0.05) and the expression of transforming growth factor beta 1 (P<0.05) also decreased significantly in the Early and Late groups. Those changes were more obviously in the Early group than in the Late group. Conclusions: Intradetrusor botulinum toxin A injection reduced bladder fibrosis in rats with spinal cord injury (SCI), which was more obviously in the Early group than in the Late group. The mechanisms might be mediated by suppression of transforming growth factor beta 1 (TGF-beta 1) expression.