Objective To study the effect of hirudo extract liquor (HEL) on activities of tissue-type plasminogen activator (tPA) and plasminogen activator inhibitor-1 (PAI-1), and levels of tPA and PAI-1 in microvascular endothelial cells of the rat cerebral cortex.Methods The experimental model of brain microvascular endothelial cells (BMEC) of Wistar rat cerebral cortex was prepared in vitro. Cell morphology was observed under the inverted phase contrast microscope and cell activity was measured with MTT assay after BMEC exposure to the concentrations of HEL ranging from 0.0625 to 8 mg/μl. The biochemical index, including activitives and levels of tPA and PAI-1 in cultured supernatants, as well as variation of semi-quantification of tPA, PAI-1 mRNA levels were measured in BMEC by reverse transcription polymerase chain reaction (RT-PCR) in the HEL treatment group and the control group normal saline treatment. The activities of tPA and PAI were measured by colorimetric assay. The contents of tPA and PAI-1 were determined using specific ELISA. The expression of tPA protein in BMEC was measured by immunohistochemistry.Results HEL of the concentrations ranging from 0.25 to 1 mg/μl promoted BMEC proliferation in a dose-dependent manner. Compared with the control group, HEL treatnent increased the content, and activity of tPA in cultured supernatants and tPA mRNA expression in BMEC, and also increased the expression of tPA protein immunoreactivity.Conclusions HEL could activate local endogenous fibrinolytic system in vitro.