Abstract: Objective: to observe the urinary plasminogen activator （PA） excretion in 5/6 nephrectomized rats. Methods: Light and electronic microscopic examination of the kidney were carried out at different time points after 5/6 nephrectomy, and urinary PA excretion rate as well as blood and urine biochemical parameters were dynamically observed.Results: Two weeks after 5/6 nephrectomy, acute renal failure induced by renal mass loss occurred, but renal pathologic changes was minimal. In this stage, the urinary PA activity of some rats decreased, but that of the others maintained normal level despite the renal mass loss. Four weeks after 5/6 nephrectomy, glomerular hypertrophy and mesangial proliferation became the characterized pathological changes,and the serum creatinine was nearly normal. In this stage, urinary PA activity decreased in some, and normalized or even increased in the others. Six to eight weeks after 5/6 nephrectomy, chronic renal insufficiency and heavey proteinuria occurred, renal pathology was characterized by focal and segmental glomerulosclerosis, as well as progressive tubulo-interstitial changes. In this stage, urinary PA excretion increased gradually, and total urinary PA output increased significantly at 8 weeks after 5/6 nephrectomy comparing with the sham operated group, P ＜0.05.Conclusion: 5/6 nephrectomy might trigger the compensatory increase of PA excretion in urine.