Transforming growth factor-β1 (TGF-β1) signaling has been shown to play a critical role in the development of diabetic nephropathy (DN). The nuclear transcription co-repressor Ski-related novel protein N (SnoN) is an important negative regulator of TGF-β1/Smad signal transduction, and subsequent biological responses including tubule epithelial-mesenchymal transition (EMT), extracellular matrix accumulation and tubulointerstitial fibrosis. Oxymatrine (OM) is an alkaloid extracted from the Chinese herb Sophora japonica and has been demonstrated to prevent fibrosis. However, the anti-fibrosis effect of OM in DN is still unclear. In this study, we cultured normal rat renal tubular epithelial cells (NRK52Es) in high glucose and high glucose plus OM, and detected the expression of E-cadherin, α-SMA, FN, TGF-β1, SnoN, Arkadia, p-Smad2 and p-Smad3 and poly-ubiquitination of SnoN. The results showed that E-cadherin and SnoN expression in NRK52Es decreased significantly, but poly-ubiquitination of SnoN, TGF-β1, α-SMA, FN, Arkadia, p-Smad2 and p-Smad3 expression significantly increased due to high glucose stimulation, which could be almost completely reversed by OM, suggesting that OM may alleviate EMT induced by high glucose via upregulating SnoN expression and inhibiting TGF-β1/Smad signaling pathway activation. Hence, OM could be a novel therapeutic for DN.