Objective To investigate miR-146b-5p expression in mice model of renal fibrosis induced by unilateral renal ureteral ligation, and to suppress miR-146b-5p expression to improve renal fibrosis induced by unilateral renal ureteral ligation in mice. Methods Twenty-four 8-week-old C57BL/ 6 male mice were randomly divided into sham operation group (sham), UUO model group (UUO), UUO+kidney miR-146b-5p knockdown group (UUO-KD), 8 mice in each group. In the sham group,the skin was only cut to expose and free the right kidney and ureter without ligation or disconnection. In the UUO group, the animal model of unilateral ureteral obstruction (UUO) was performed. In the UUOKD group, miR-146b-5p was specificly knocked down by electrotransferring the CRISPR/ RfxCas13 d plasmid in the mouse kidney. After 24 hours, the UUO mouse model was established according to the method of the model group, and the mice were sacrificed 7 days later to collect kidney samples. HE staining was used to observe renal pathological changes, Masson was used to detect the degree of renal interstitial fibrosis, immunohistochemistry was used to detect the expression of fibrosis-related proteins (α-SMA, FN, Col-1), and Western Blot and Real-time PCR were used to detect miR-146b-5p,α-SMA, FN, IL-1β, IL-6, TNF-α and other gene changes. Results Real-time PCR showed that miR-146b-5p was significantly increased in UUO model, and the gene was significantly decreased after electroporation knockdown of miR-146b-5p (P< 0. 05). Meanwhile,the expression of IL-1β, IL-6, TNF-α and other inflammatory factors was significantly down-regulated (P< 0. 05). It was observed after HE and Masson staining. Compared with the UUO group, the UUO-KD group had a better kidney structure, slightly deformed renal tubules, and less severe renal damage. The degree of fibrosis was significantly improved. And the results of immunohistochemistry showed that α-SMA, FN, Col-1 and other fibrosis indicators were also significantly reduced in the UUO-KD group ( P< 0. 0001). Conclusions Inhibition of highly expressed miR-146b-5p in UUO can significantly improve renal fibrosis, and miR-146b-5p may be a potential therapeutic target for renal fibrosis.