Objective: The aim of this study is to elucidate regulatory mechanism of IGFBP-2 expression and its physiological roles in mice and humans. Methods: To determine the potential role of Igfbp-2 in obese and diabetic states, we estimated its expression level in mouse liver and compared global mRNA expression patterns in the primary hepatocytes by gene profiling. And we investigated whether metformin modulates the promoter activity of mouse Igfbp-2. To elucidate the relationship between metformin and hormonal profile in diabetic patients, the biochemical characteristics and serum levels of IGFBP-2 and IGF-1 of metformin-treated and type 2 diabetes mellitus patients were examined. Results: The expression levels of hepatic Igfbp-2 and lipogenic genes were significantly increased in db/db mice and the metformin-stimulated primary hepatocytes. Additionally, metformin treatment increased IGFBP-2 secretion in primary hepatocytes isolated from WT mice, whereas AMPK- or Sirt1-silenced primary hepatocytes exhibited significantly reduced IGFBP-2 secretion compared with primary hepatocytes from Pparα-null mice. Moreover, metformin promoted IGF-1R and Akt phosphorylation caused by IGF-1 in WT mice but not in Pparα null mice. Finally, serum IGFBP-2 level was markedly reduced in diabetic patients and circulating IGFBP-2 level was re-established upon metformin treatment, in comparison with diabetic patients; Otherwise, metformin treatment suppressed an increased IGF-1 level in diabetic patients. Conclusion: In conclusion, we demonstrated that upregulation of Igfbp-2 by metformin activates the AMPK-Sirt1-PPARα signaling network both in vivo and in vitro. Moreover, our results suggest that metformin affects IGF-1 homeostasis by modulating IGF-1 bioactivity in the liver. We speculate that the metformin- AMPK-Sirt1-PPARα cascade network ameliorates metabolic dysfunction by balancing the IGFBP-2-IGF-1 signaling system in diabetic mice and patients. Therefore regulation of the IGFBP-2-IGF-1 axis by an AMPK activator may represent a molecular mechanism to control IGF-1 homeostasis.