Fuzhengfangaitang (FZFAT) is used to inhibit recurrence and metastasis of cancer in the clinic. By applying an in vitro invasion assay model, we examined the antimetastatic effect of FZFAT. In the 3H-thymidine incorporation assay, FZFAT-treated groups showed a decreased DNA synthesis rate compared with the control group (F-value 87.42981, P-value 2.02E-08, F0.05(3,12) 3.4903). Gelatin zymogram assay showed that FZFAT decreased the gelatinolytic activity of matrix metalloproteinases-9 (MMP-9) from human fibrosarcoma cell line (HT-1080), at concentrations of 200 and 400 microg/ml. In the MMPs dot blotting assay, FZFAT inhibited the expression of MMP-1 at concentration of 100 microg/ml, and MMP-9 at concentrations of 200 and 400 microg/ml. Western blots for AP-1 and its signal mediators Erk and JNK showed that expression of Fos and JNK were decreased by the addition of FZFAT at 300 microg/ml, whereas Erk was not. Therefore it was evident that FZFAT regulated the expression of MMP-9 through its transcription factor AP-1 and the signal mediator JNK. We examined whether FZFAT inhibited the invasion of HT-1080 cells through matrigel precoated transwell chambers. The results showed that FZFAT effectively inhibited the invasion of HT-1080 cells as compared with the control phorbol 12-myristate-13-acetate (+PMA) groups (t-value 5.871584, P-value 0.013901, t0.05(2) 2.919987). From our research, part of the mechanism underlying the antimetastatic effect of FZFAT has been elucidated in vitro.