Abstract: Objective To investigate the expression of SUMO2/3 and Smad4 in rat glomerular mesangial cells (GMCs) induced by high glucose, and the interaction between small ubiquitin related modifier （SUMO）2/3 and Smad4; and to explore the role and mechanism of sumoylation in regulating TGF-β signaling in diabetic nephropathy. Methods Cultured rat GMCs were divided into five groups: normal glucose group (5.6 mmol/L glucose), high glucose groups (10, 20 and 30 mmol/L glucose), and mannitol group (osmotic control). The expression of SUMO2/3, Smad4 and fibronectin (FN) was measured by Western blot and RT-PCR. The interaction and colocalization between SUMO2/3 and Smad4 were detected by Co-immunoprecipitation and immunofluorescence confocal laser microscopy. Results Compared with controls, the expressions of SUMO2/3, Smad4 and FN in the cells in the high glucose groups increased (P<0.05). The co-immunoprecipitation and immunofluorescence confocal laser scanning showed that Smad4 interacted and colocalized with SUMO2/3 and the sumolyation (SUMO2/3) of Smad4 was enhanced significantly in the high glucose groups compared with the control group (P<0.05). Conclusion Sumolyation of Samd4 by SUMO2/3 may be involved in the regulation of TGF-β signaling in diabetic nephropathy.