Abstract: AIM To clarify whether collagen deposition and collagen synthesis are increased in renovascular hypertensive rats (RHR) and whether these are affected by treatment with tetrandrine (Tet). METHODS Collagen deposition was detected by electron microscope and evaluated by the amount of hydroxyproline in aorta of sham operated rats (Sham), renovascular hypertensive rats (RHR), and Tet treated RHR. The aortic vascular smooth muscle cells (AVSMCs) were isolated and cultured. The collagen synthesis in cultured AVSMCs was detected by ³H-proline incorporation. RESULTS The ultrastructure of aorta suggests that AVSMCs in RHR had been transferred from contractile phenotype to synthetic phenotype. Compared with sham operated rats, the hydroxyproline content in aorta was increased by 36.6% in RHR, while it was reduced by 18.7% in Tet treated RHR (P<0.01,vs RHR). Tet (0.1-10 μmol·L^-1) treatment in vitro induced a concentration dependent depression in ³H-proline incorperation stimulated by NE or Ang II in AVSMCs from either Sham or RHR. CONCLUSION The depressive effects of tetrandrine on collagen synthesis and deposition in arteries may contribute to the regression of vascular remodeling.