Objective:To explore the molecular mechanisms of antitumor properties of triptolide, a bioactive component isolated from the Chinese herb Tripterygium wolfordii Hook F. Methods:Human fibrosarcoma HT-1080 cells were treated with different doses of triptolide for 72 h. Then the expression and activity of matrix metalloproteinase (MMP)-2 and -9 were measured and the invasiveness of triptolide-treated HT-1080 cells was compared with that of anti-MMP-9-treated HT-1080 cells. Results:18 nmol/L triptolide inhibited the gene expression and activity of MMP-9, but not those of MMP-2, in HT-1080 cells. In addition, both 18 nmol/L triptolide and 3μg/mL anti-MMP-9 significantly reduced the invasive potential of HT-1080 cells, by about 50%and 35%, respectively, compared with the control. Whereas there was no significant difference between the effect of 18 nmol/L triptolide and that of anti-MMP-9 on invasive potential of HT-1080 cells. Conclusions:These data suggest that triptolide inhibits tumor cell invasion partly by reducing MMP-9 gene expression and activity.