A growing body of evidence suggests that low serum level of adiponectin is a high risk factor for various cancers including prostate, colorectal, endometrial, and breast cancer. However, little is known about the molecular mechanism by which adiponectin inhibits proliferation and metastasis of cancer cells. Therefore, the expression levels of metastasis-associated genes such as urokinase-type plasminogen activator, matrix metalloprotease 2 and 9 were examined. These metastasis-associated genes were suppressed and the activities of these proteins were also decreased by the treatment of adiponectin while the level of metastasis suppressor gene, tissue inhibitor of MMP1, was significantly increased in human breast cancer cell line MDA-MB-231. To elucidate signaling pathway underlying adiponectin-mediated the suppression of breast cancer cell metastasis, the phosphorylation levels of AKT was examined because AKT plays a critical role in the regulation of MMP expression. The phosphorylated AKT levels were dramatically decreased while AMPK phosphorylation was conversely greatly increased by the treatment of adiponectin. These results suggest that the activated AMPK increases activity of a protein phosphatase, which decreases AKT phosphorylation. The adiponectin-induced AMPK activation was markedly increased PP2A activity, leading to the dephosphorylation of AKT. Taken together, these results showed that adiponectin-activated AMPK increased the activity of PP2A and that the activated PP2A-induced AKT dephosphorylation was underlying mechanism by which adiponectin suppresses the expression of metastasis associated genes.