Objective: To observe the inhibiting effects of an antisense u-PAR vector on invasion by highly invasive PC-3M cell subclones. Methods: The effects of an antisense vector on invasion by highly invasive PC-3M cell subclones were observed and compared in vitro by monolayer invasion assay and soft agar clone. Then, both a quantitative RT-PCR and zymography were used to exam the effects of the antisense u-PAR on activity of MMP-9 in those highly invasive cell subclones. Furthermore, the tumorigenesis rate and invasions by the cell subclones with or without the antisense u-PAR were observed in nude mice. Results: It is found that the speed of growth in vitro was slowing down by highly invasive PC-3M cell subclones transfected with the antisense u-PAR, and the ability of anchorage-independent growth of those cell subclones was also decreasing sharply,and the inhibiting rate was 79% and 60%, respectively. Although the antisense u-PAR didn′t change MMP-9 gene transcription, but they could inhibit the activation of MMP-9 of highly invasive PC-3M cell subclones. Moreover, the tumorigenesis rate of the cell subclones with the antisense u-PAR decreased and the growth of a neoplasm also slowed down. The t tests showed the difference between experimental and control groups reached statistical significance ( P