Nephropathy is one of the most common complications of diabetes mellitus which remains incompletely understood. We reported the expression of myosin light chain kinase (MLCK) in the kidney of diabetic rats and investigated the correlation between MLCK and diabetic nephropathy by observing the expression of MLCK. The diabetic model rats were induced by an intraperitoneal injection of streptozotocin (STZ) and the insulin-treated rats were subcutaneously injected with protamine zine insulin 3u/d. The kidneys were excised and immersed in 4% polyoxymethylene after 12 weeks later. The expression of MLCK was analyzed by immunohistochemical staining and Western blot. Immunohistochemical analysis and Western blot assay indicated that the MLCK expression was higher in kidney of diabetic rats than that in control and it was decreased in kidney of insulin-treated rats. Our results suggested that the over expression of MLCK may be related with the development of diabetic nephropathy.