Plasminogen activator inhibitor type 1 (PAI-1) is a serine protease inhibitor (Serpine 1), and it inhibits both tissue plasminogen activator and urokinase plasminogen activator which are important in fibrinolysis. We aimed to find whether there is a possible association between PAI-1 level, PAI-1 4G/5G polymorphism, and endometrial cancer. PAI-1 levels in peripheral blood were determined in 82 patients with endometrial carcinoma and 76 female healthy controls using an enzyme-linked immunoassay (ELISA). Then, the genomic DNA was extracted and screened by reverse hybridization procedure (Strip assay) to detect PAI 1 4G/5G polymorphism. The levels of PAI-1 in the patients were higher statistically in comparison to controls (P < 0.001). The distribution of PAI-1 4G/5G polymorphism was quite different between patients and controls (P = 0.008), and 4G allelic frequency was significantly higher in the patients of endometrial cancer than in controls (P = 0.026). We found significant difference between Grade 1 and Grade 2+3 patients in terms of the PAI-1 levels (P = 0.047). There was no association between PAI-1 4G/5G polymorphism and the grades of endometrial cancer (P = 0.993). Our data suggest that the level of PAI-1 and PAI-1 4G/5G gene polymorphism are effective in the formation of endometrial cancer. PAI-1 levels are also associated with the grades of endometrial cancer.