Aim: To design and screen antisense oligodeoxynucleotides (ASODNs), which inhibit type-1 plasminogen activator inhibitor (PAI-1) expression in human umbilical vein endothelial cells (HUVEC) in vitro. Methods: Twenty seven ASODNs against different sites of PAI-1 mRNA were designed and transfected to HUVEC by lipofectin in vitro. The effects of ASODNs on PAI-1 antigen, PAI-1 activity and PAI-1 mRNA expression were detected by ELISA, amidolytical assay and RT-PCR, respectively. Results: Transforming growth factor β1 (TGF-β1)-treated HUVEC increased the expression of PAI-1 compared with the normal HUVEC. Five among twenty seven designed ASODNs were effective in inhibiting the increase in PAI-1 antigen and PAI-1 activity in a dose-dependent manner after 48-h transfection. In particular, ASODN 14 (AO14) exhibited the best inhibitory effect. The control sequences of AO14, including sense, scramble, and mismatch sequences, did not significantly inhibit PAI-1 activity. It was revealed that the inhibitory efficacy of AO14 was in a sequence-specific manner. RT-PCR showed that ASODN 1, 7, 8, 14, and 15 decreased PAI-1 mRNA expression induced by TGF-β1 and AO14 showed the best inhibitory effect. Conclusion: ASODN 1,7,8, 14, and 15, among twenty seven designed ASODNs against PAI-1 mRNA, significantly decreased PAI-1 antigen and PAI-1 activity induced by TGF-β1 in a dosedependent manner in HUVEC in vitro. AO14 showed the best inhibitory effect on PAI-1 expression in a sequence-specific manner. The results of RT-PCR indicated that inhibitory effects of ASODNs on PAI-1 biosynthesis occurred at the mRNA level. Four among five effective target sites of ASODNs located at the translation initiation site or within the translation area of PAI-1 mRNA, suggesting that these sites may be promising sites for the design of effective ASODNs.