BACKGROUND: Recent study found that microRNA (miRNA) are involved in diabetic kidney disease (DKD). The objective of this study is to determine the role of miR302a-3p in the process of renal epithelial-mesenchymal transition (EMT) in DKD. METHODS: The miRNA expression profiling of the cell line stimulated by high glucose was performed by a microarray analysis. Then real-time polymerase chain reaction (PCR) were used to determine the expression of one of the miRNAs significantly upregulated in cell line stimulated by high glucose, miR302a-3p. miR302a-3p mimics and inhibitor were transfected to HK-2 cells following exposure to high glucose and normal glucose, respectively. The expressions of E-cadherin, vimentin, and Zinc finger E-box-binding protein 1 (ZEB-1) were determined by real-time PCR and Western blot. Finally, the levels of miR302a-3p in the plasma of DKD patients were detected by real-time PCR, and then the relationship of miR302a-3p and urinary albumin excretion (UAE) or estimated glomerular filtration rate (eGFR) was analyzed. RESULTS: The expression of miR-302a-3p, 513a-5p, 1291 and the other 17 miRNA were increased significantly in HK-2 cell line after high glucose stimulation; on the other hand, miRNA490-3p, 638, 3203 and the other 19 miRNA were decreased significantly. In vitro, miR-302a-3p expression in HG group increased at 6 h and ascended to the highest level at 12 and 24 h and then gradually decreased from 48 to 72 h. More interesting, ZEB1 protein expression had an opposite change, which gradually decreased from 6 to 24 h and then gradually increased from 48 to 72 h. Moreover, overexpression of miR-302a-3p suppressed expression of ZEB1 in the post-transcriptional level and reversed high glucose-mediated downregulation of E-cadherin and upregulation of vimentin. Meanwhile, loss of miR-302a-3p expression can lead to EMT of HK-2 cells just as high glucose stimulation. Further study demonstrated that the expression of circulating miR-302a-3p was significantly increased in the diabetes mellitus (DM) with normoalbuminuria (DM group, n = 22) compared with control (healthy persons, n = 30) and then decreased in DM with microalbuminuria (DNE group, n = 20). Furthermore, its expression in DM with macroalbuminuria (DNC group, n = 18) was decreased significantly compared with DM group. Circulating miR-302a-3p had negative relevance with UAE in DNE group (r = -0.649, p = 0.002) and DNC group (r = -0.681, p = 0.006). Circulating miR-302a-3p had positive relevance with eGFR in DNC group (r = 0.486, p = 0.041). CONCLUSIONS: These findings suggest that miR-302a-3p may play a protective role by targeting ZEB1 in renal EMT in DKD. In view of these findings, it is conceivable that miR-302a-3p may serve as a potential novel target in pre-EMT states for the amelioration renal fibrosis seen in DKD.