Yanhusuo (Corydalis yanhusuo W.T. Wang) is a well-known traditional Chinese medicine (TCM). In this study, we attempted to characterize in detail the signaling cascades that produce its anti-metastatic effect on the human breast cancer cell line, MDA-MB-231. We found that the yanhusuo extract inhibited the migration and invasion of MDA-MB-231 cells in vitro. In addition, the yanhusuo extract inhibited the mRNA expression and activity of metalloproteinase-9 (MMP-9). The anti-cancer metastasis effect of yanhusuo involved the activation of p38 and inhibition of ERK1/2 and SAPK/JNK mitogen-activated protein kinase (MAPK) signaling. Our experiments identified the biological activity of yanhusuo against cancer metastasis in vitro and provide a rationale for its further investigation.