Objective To observe the effect of miR⁃let⁃7c inhibitor on spermatogonial stem cells（SSCs） by transfecting it on the differentiation of SSCs and sperm quality in mice. Methods SSCs were isolated from testes of neonate mice（3~6 days old），and their purities were performed by flow cytometry with ID4 and Thy1 markers. Cultured cells were transfected with miR⁃let⁃7c inhibitor. Evaluation of the proliferation（GFRa1，PLZF，and ID4） and differentiation（C⁃Kit）markers of SSCs were accomplished by immunocytochemistry and western blot 48h after transfection. In vivo experiments，60 mg/（kg·d）intraperitoneal injection of cyclophosphamide was used to prepare a mouse model of oligoasthenospermia，and SSCs transfected with miR⁃let⁃7c inhibitor were injected into the epidid⁃ ymis to observe the changes of spermatogenic cells and interstitial cells and analyze sperm concentration，vitality and morphology. Results The expression of differentiation markers of SSCs after transfection in the miR⁃let⁃7c inhibitor group was significantly increased；the protein of GFRa1，PLZF，and ID4 was decreased，and the sperm concentration，sperm motility and regular morphological rate of oligoasthenospermia mice were significantly in⁃ creased. Conclusion miR⁃let⁃7c inhibitor promotes the differentiation of spermatogonial stem cells and improves sperm quality in mice.