To study the effects of tetrandrine (Tet) on hypertrophied myocardial hydroxyproline content and myosin ATPase activity, left ventricular hypertrophy(LVH) was induced by renovascular hypertension (two-kidney, one-clip) in rats. Eight weeks after operation Tet 50 mg*kg-1*d-1 and enalapril(Ena) 6 mg*kg-1*d-1 were given by gavage for 8 weeks. The results showed that hydroxyproline content in LVH group was much higher than that of sham-operated one 〔(5.9±0.3) vs (3.6±0.4) mg*g-1 dry weight〕, and was decreased by 28.2% and 39.0% in Tet and Ena groups, respectively. Myosin ATPase activity in LVH group was much lower than that of sham-operated group 〔(0.43±0.09) vs (0.97±0.06) mmol Pi*min-1*g-1 protein, P<0.01〕. In Tet and Ena groups they were 60.5% and 118.6% higher than that of LVH group, respectively. The results suggest that Tet or Ena partially reduce the hydroxyproline content and elevate myosin ATPase activity of hypertrophied myocardium in renovascular hypertensive rats.