Objectives　To study the expression characteristics of miR-125a-5P in medulloblastoma, and its role as tumor suppressor. Methods　The miR-125a-5p level was detected by stem loop Real-time RT-PCR in 58 cases of medulloblastoma tissues and 2 medulloblastoma cell lines, D341 and Daoy cells. miR-125a-5P oligonucleotide was transfected to D341 cells, then Ki-67 expression was detected by immunofluorescence assay, cell migration was tested by transwell assay, and tumorigenicity was determined by clone formation assay. The inhibitory effect of miR-125a-5p on medulloblastoma cells in vivo was detected in tumor bearing mice model. Results　The relative expression level of miR-125a-5P in medulloblastoma tissues was significantly higher than that of normal children's brain tissue (t=17.545, P<0.01), while the expression level of miR-125a-5P in 2 medulloblastoma cells were significantly lower than other control cells (F=9.437, P<0.01). The expression level of miR-125a-5P was significantly higher than that of the neural stem cells, D341 and Daoy cells, and the difference was statistically significant (P<0.05). Compared with the control group and the non-sense group, the ability of proliferation, migration and clone of cells in miR-125a-5p group obviously declined (P <0.05), as well as the tumor volume in mice (P<0.05). Conclusions　The expression of miR-125a-5P in medulloblastoma was reduced or absent, and was supposedly a tumor suppressor gene.