Objective：To observe the effects of transfection of Gremlin plasmid and Gremlin siRNA plasmid in vitro on expression of mouse mesangial cells（MMCs），bromodeoxyuridine（BrdU） and collagen Ⅳ. Methods：Cultured MMCs were divided into 7 groups：normal glucose group（NG，5.5 mmol/L），normal glucose plus mannitol group（NG+M，24.5 mmol/L mannitol），normal glucose plus emp－ty vector group（NG+V），normal glucose plus Gremlin expression plasmid group（NG+P）/normal glucose plus Gremlin siRNA plas－mid group（NG+Gremlin si），high glucose group（HG，30 mmol/L），high glucose plus empty vector group（HG+V） and high glucose plus Gremlin expression plasmid group（HG+P）/high glucose plus Gremlin siRNA plasmid group（HG+Gremlin si）. Cell proliferation was examined using BrdU ELISA and accumulation of collagen Ⅳ was measured using radioimmunoassay at 24 h after high glucose stimulation. Results：Expression of BrdU and collagen Ⅳ in the supernatant was increased in NG+P and HG group compared with that in NG group（all P=0.000）. Expression of BrdU and collagen Ⅳ was up-regulated in HG+P group than in HG group（all P=0.000）. Inhibition of Gremlin with Gremlin siRNA plasmid reversed HG-induced abnormalities（increase in BrdU expression and collagen Ⅳ concentration）（all P=0.000）. Conclusions：Gremlin induces cell proliferation and accumulation of collagen Ⅳ in MMCs.Gremlin plays an important role in the development of diabetic nephropathy.