In breast cancer, metastasis is the main reason for patient mortality. In the present study, we used breast cancer MDA-MB-231 cells and a mouse xenograft model to demonstrate the effect of emodin on the migration, invasion and metastasis of human breast cancer MDA-MB-231 cells and the related mechanisms. In vitro, wound healing and Transwell assays showed that emodin dose-dependently inhibited the migration and invasion of MDA-MB-231 cells. Enzyme-linked immunosorbent assay (ELISA) showed that emodin decreased the secretion of MMP-2 and MMP-9. Western blot analysis showed that emodin downregulated the expression levels of MMP-2, MMP-9, uPA and uPAR as well as p38 inhibitor SB203580 and ERK inhibitor PD980559, even though TIMP-1 and TIMP-2 were not obviously changed in the MDA-MB-231 cells. Furthermore, emodin inhibited the activity of p38 and ERK1/2 in the MDA-MB-231 cells. In vivo, emodin inhibited lung metastasis in mice bearing the breast cancer MDA-MB-231 xenografts with no obvious changes in body weight, liver and kidney functions. These results indicated that emodin inhibited the lung metastasis of human breast cancer in a mouse xenograft model, and inhibited the invasion of MDA-MB-231 cells associated with the downregulation of MMP-2, MMP-9, uPA and uPAR expression as well as decreased activity of p38 and ERK.