Objective To investigate the effect of vitamin D (VD) on epithelial mesenchymal transition (EMT) of renal tubular epithelial cells in infant rats with hypothyroidism (HT) and its regulatory mechanism on tumor necrosis factor receptor related factor 6 (Traf6)/transforming growth factor β activated kinase 1 (TAK1) pathway. Methods Propylthiouracil (PTU) was used to establish the HT model of infant rat by intragastric administration. Overexpression of TAK1 (pc DNA3.1-TAK1) was used to perform the functional salvage experiment. The animals were divided into normal group, HT group, VD low dose (HT+VD-L) group, VD high dose (HT+VD-H) group and HT+VD-H+pc DNA3.1-TAK1 (HT+VD-H+pc) group with 10 rats in each group. Automatic biochemical analyzer was used to detect the contents of creatinine (Scr) and blood urea nitrogen (BUN) in serum. Terminal-deoxynucleoitidyl transferase-mediated nick end labeling was used to detect the apoptosis in renal tissue. Immunohistochemistry was used to detect the expressions of transforming growth factor-β1 (TGF-β1), α-smooth muscle actin (α-SMA) and E-cadherin (E-cadherin) in renal tissue. Western blot was used to detect the expressions of B cell lymphoma-2(Bcl-2), Bcl2-associated x protein(Bax), Traf6, TAK1 and phosphorylated TAK1 (p-TAK1) in renal tissue. 〖WTHZ〗Results VD could significantly decrease the contents of Scr and BUN in serum, down-regulate the rate of apoptosis in renal tissue, decrease the expression of TGF-β1 and α-SMA in renal tissue, up-regulate the expression of E-cadherin, inhibit the expression of Traf6, p-TAK1 and Bax in renal tissue, and increase the expression of Bcl-2 in renal tissue.And the differences were statistically significant (all P＜0.05).Conclusion Vitamin D can inhibit the EMT of renal tubular epithelial cells, reduce the rate of apoptosis in renal tissue, reduce the pathological injury of renal tissue and improve renal function in infant rats with HT, which is related to the inhibition of the activation of Traf6/TAK1 signaling pathway