Glomerular hypertrophy and progressive expansion of extracelluar matrix (ECM) have been regarded as the early feature of diabetic nephropathy (DN), which leads to accumulation of ECM and thickening of glomerular basement membrane, and subsequently induces renal fibrosis. Both increasing synthesis and decreasing degradation of matrix components are responsible for matrix accumulation. The later may play more important role in DN that involves a number of matrix metalloproteinases (MMPs). MMPs are a family of proteolytic enzymes whose activity is tightly regulated by tissue inhibitor of metalloproteinases (TIMPs), and the MMP/TIMP ratio is critical for coordinating matrix production and degradation. 1 Recently, considerable evidence suggests that the intrarenal renin-angiotensin system plays an important role in the development of DN. 2 Blockade of the renin-angiotensin system (RAS) by angiotensin-coverting enzyme inhibitor (ACEI) or angiotensin Ⅱ receptor antagonist (AIIRA) delays the progression of renal injury associated with diabetes. 3 AIIRA has been regarded as the first line choice for DN therapy. However, the potential mechanism for AIIRA in the ECM degradative pathway has not been fully elucidated. The present study is to investigate the effect of Irbesartan (Irb), a newly developed AIIRA, on renal expression of MMP-2 and TIMP-2 in streptozotocin (STZ)-induced diabetic rats. Glomerular hypertrophy and progressive expansion of extracelluar matrix (ECM) have been considered as the early feature of diabetic nephropathy (DN), which leads to accumulation of ECM and thickening of glomerular basement membrane, and subsequently induces renal fibrosis. Both increasing synthesis and decreasing degradation The later may play more important role in DN that involves a number of matrix metalloproteinases (MMPs). MMPs are a family of proteolytic enzymes whose activity is tightly regulated by tissue inhibitor of metalloproteinases (TIMPs), and the MMP / TIMP ratio is critical for coordinating matrix production and degradation. 1 Recently, considerably evidence suggests that the intrarenal renin-angiotensin system plays an important role in the development of DN. 2 Blockade of the renin-angiotensin system (RAS) by angiotensin-coverting enzyme inhibitor (ACEI) or angiotensin II receptor antagonist (AIIRA) de lays the progression of renal injury associated with diabetes. However, the potential mechanism for AIIRA in the ECM degradative pathway has not been fully elucidated. The present study is to investigate the effect of Irbesartan (Irb), a newly developed AIIRA, on renal expression of MMP-2 and TIMP-2 in streptozotocin (STZ) -induced diabetic rats.