〔Abstract〕 Objective To investigate the effect of miR-21 on STAT3 signaling pathway on the proliferation and migration of nephroblastoma cells. Methods The expression of miR-21 was detected by RT-PCR in human nephroblastoma and paracancerous tissues. Human nephroblastoma cells were divided into three groups: Blank group, si-miR-21 group(transfected with si-miR-21) and si-miR-21 NC group(transfected with si-miR-21 NC). The expressions of related proteins and apoptosis related proteins in STAT3 signaling pathway were detected by Western blot.The cell proliferation activity was detected by MTS. The cell apoptosis was detected by flow cytometry, and the cell migration ability was detected by Transwell. Results The relative expression of miR-21 in human nephroblastoma was significantly higher than that in adjacent tissues(P<0.05). After transfection, there were significant differences in the relative expression of p-STAT3, Bcl-2, Bcl-xl, A490 absorbance value and cell migration number among the three groups(P<0.001). Compared with the Blank group, si-miR-21 group increased(P<0.05), si-miR-21 NC group decreased(P<0.05). There were significant differences in cell apoptosis among the three groups(P<0.001).Compared with the Blank group, si-miR-21 group decreased(P<0.05), si-miR-21 NC group increased(P<0.05). miR-21 was positively correlated with p-STAT3, Bcl-2 and Bcl-xl(r=0.824, 0.778, 0.837;P<0.001). Conclusion Over expression of miR-21 can promote the proliferation and migration of nephroblastoma cells, which may be due to the up regulation of STAT3 signaling pathway.