Glomerular sclerosis is characterized by mesangial cell proliferation and progressive extracellular matrix (ECM) accumulation. CCN3 belongs to the CCN family of matrix proteins; increasing evidence suggests that CCN3 is an endogenous negative regulator of the ECM and fibrosis. However, the exact role of CCN3 in the accumulation of ECM remains unknown. The aim of the present study was to investigate the effects of CCN3 on TGF-β1-induced production of ECM in human mesangial cells (HMCs) in vitro. Treatment with TGF-β1 (0.5-2.0 ng/mL) suppressed the mRNA and protein expression of CCN3 in HMCs in dose- and time-dependent manners. Furthermore, treatment with TGF-β1 significantly increased the expression of the two markers of renal fibrosis, fibronectin (FN) and type I collagen (COLI), in HMCs. Moreover, treatment with TGF-β1 significantly decreased the expression of metalloproteinase (MMP)-2 and MMP-9, and markedly increased the expression of tissue inhibitor of metalloproteinase (TIMP)-1 in HMCs. Pretreatment of HMCs with exogenous CCN3 (5-500 ng/mL) or overexpression of CCN3 significantly attenuated TGF-β1-induced changes in FN, COLI, MMP-2, MMP-9 and TIMP-1 in HMCs. These results suggest that CCN3 suppresses TGF-β1-induced accumulation of ECM in HMCs. CCN3 may have potential as a novel therapeutic target for alleviating glomerulosclerosis.