Objective: To investigate the effects of miR-125a-5p targeting signal transducer and activator of transcription-3 (STAT3) on proliferation and invasion of renal cancer cells, and to preliminarily analyze the action mechanism. Methods: During the period from March 2017 to February 2018, 48 pairs of cancer tissues and corresponding normal adjacent tissues (more than 3 cm away from the tumor margin) resected from patients underwent renal cancer surgery at the Department of Urology, the Air Force Hospital of the Northern War Zone were collected for this study. Normal renal HK-2 cells and renal cancer cells (A498, GRC-1, 786-O and ACHN) were cultured in vitro. The expression of miR-125a-5p in above mentioned tissues and cells was detected by qPCR. miR-125a-5p-NC, miR-125a-5p-mimics, pLV-STAT3 and pLV-STAT3 with miR-125a-5p mimics were transfected intoA498 cells, namely NC group (negative control group), miR-125a-5p-mimics group, pLV-STAT3 group and pLV-STAT3+mimics group. The normally cultured A498 cells were used as blank control (Ctrl group). qPCR was performed to detect them RNA expressions of miR-125a-5p and STAT3 in cells of all groups. The bioinformatics prediction software and Dual luciferase assay were performed to analyze the targeting relationship between miR-125a-5p and STAT3. CCK-8, Flow cytometry, Transwell chamber assay were performed to detect cell proliferation activity, apoptosisand invasion, respectively. The expressions of STAT3, Bcl-2, BAX, cleaved cysteinyl aspartate specific proteinase 3 (cl-caspase-3), tumor suppressor gene p21, N-cadherin, E-cadherin, VEGF and HIF-1 in the cells were detected by WB. Results: The expression of miR-125a-5p in renal cancer tissues and cells was significantly lower than that in adjacent normal tissues and normal renal cells (all P<0.05). Compared with NC group, expression of miR-125a-5p in A498 cells transfected with miR-125a-5p-mimics was significantly increased, while expression of STAT3 mRNA was significantly decreased (all P<0.05). STAT3 was the target gene of miR-125a5p. Compared with NC group, cell viability, number of invasive cells, expressions of Bcl-2, N-cadherin, VEGF, HIF-1, and STAT3 as well as its phosphorylation level in miR-125a-5p mimics group were significantly decreased (all P<0.05), while cell apoptosis and expressions of BAX, p21, cl-caspase-3 and E-cadherin were significantly increased (all P<0.05); the cell viability, number of invasive cells, expressions of Bcl-2, N-cadherin, VEGF, HIF-1 and STAT3 as well as its phosphorylation level in pLV-STAT3 group were significantly increased (all P<0.05), while cell apoptosis and expressions of BAX, p21, cl-caspase-3 and E-cadherin were significantly decreased (all P<0.05). Compared with pLV-STAT3 group, cell viability, number of invasive cells, expressions of Bcl-2, N-cadherin, VEGF, HIF-1, and STAT3 as well asits phosphorylation level were significantly decreased in pLV-STAT3 mimics group (all P<0.05), while cell apoptosis, expressions of BAX, p21, cl-caspase-3 and E-cadherin were significantly increased (all P<0.05). Conclusion: miR125a-5p shows low expression in renal cancer tissues and cells, which can inhibit proliferation and invasion of A498 cells and promote cell apoptosis by down-regulating its target gene STAT3.