•Roscovitine alleviates renal functional and histological injuries of diabetic mice.•Roscovitine attenuates renal fibrosis of diabetic mice.•Roscovitine inhibits EMT of tubular cell in diabetic mice.•Roscovitine reduces TGF-β1/p38MAPK expression to inhibit EMT in diabetic mice. Tubulointerstitial fibrosis is the hallmark of diabetic nephropathy, which is the leading cause of end-stage renal disease worldwide. Roscovitine, an inhibitor of Cdks, exhibits anti-fibrosis effects. The present study was aimed to explore the protected role of roscovitine from renal fibrosis of diabetic nephropathy. In vivo study showed that roscovitine treatment significantly ameliorated renal functional and histological injuries in diabetic mice. It was also showed that roscovitine coordinately inhibited the expression of collagen, α-SMA, TGF-β1, and retaining E-cadherin expression. At the cellular level, roscovitine treated HK2 cells cultured with high glucose. It was revealed that roscovitine successfully reduced α-SMA expression and ameliorated the decrease expression of E-cadherin, the two markers of tubular cell EMT. At the molecular level, roscovitine was found to exert this effect through inhibiting the up-regulation of TGF-β1/p38MAPK pathway in high glucose cultured HK2 cells. These study demonstrated a novel mechanism that roscovitine has the anti-fibrosis effects by inhibiting the TGF-β1/p38MAPK pathway in diabetic mice.