Abstract: Objective:To investigate the effect of amiloride on in vitro invasive activity and uPA (urokinase-type plasmin -ogen activator) system of human highly metastatic lung carcinoma cell line PGCL3. Methods:At 6 hours after treatment with amiloride at the concentrations of 25µmol/L, 50µmol/L and 100 µmol/L for PGCL3 cells, Transwell Chamber assay was performed to detect the effect of amiloride on the invasive and migratory capacity of PGCL3 cells. Effect of amiloride on the activity of uPA and PAI-1 (plasminogen activator inhibitor-1) secreted by PGCL 3 cells were measured by chromogenic sub -strate assay after PGCL3 cells were incubated with amiloride for 24hours. RT-PCR was used to analyze the effect of amilorede on mRNA levels of uPA, uPAR (urokinase-type plasminogen activator receptor) and PAI- 1. The expression levels of uPA, ERK 2 (extracellular regulated protein kinases 2) and ras protein were assessed by Western blot. Results: The num -ber of cells through membrane was significantly decreased in invasion and migration test in vitro. The inhibitory rates of in-vasion and migration after treatment with amiloride of 100 µmol/L were 37.7%±4.1% and 64.9%±4.9%, respectively, with a significant difference from those in the control group ( P<0.01). At 24hours after amiloride treatment, the chromogenic sub -strate assay showed direct inhibition of the activity of uPA and PAI- 1 secreted by PGCL3 cells. No effect on the expression of uPAR in mRNA level was observed, but the expression of PAI- 1 in mRNA level was significantly inhibited. Amiloride of 100 µmol/L dramatically inhibited the expression of uPA mRNA. The expression level of uPA protein was decreased with the increase of the concentration of amiloride, but no effect was observed on the expression of ERK 2 and ras in protein level. Conclusion:Amiloride can inhibit the invasion and migration of PGCL3 cells, through inhibiting the expression and activity of uPA and PAI- 1. Amiloride is a potential agent to inhibit cancer invasion and metastasis.