Insulin plays an important role in various metabolic as well as anabolic actions in cells, including osteoblast cells. In the present study, we explored to determine if insulin receptor could associate with syndecan-1 in response to insulin and such association could lead to the activation of subsequent ERK I/II and alkaline phosphatase (ALP) in osteoblast cells. Insulin rapidly induces the association of insulin receptor with syndecan-1. Synstatin is a specific peptide inhibitor that blocks the binding of syndecan-1 to integrate. In the presence of synstatin, insulin-stimulated ERK I/II activation was dramatically inhibited, suggesting that syndecan-1/integrin interaction is essential in the activation of ERK I/II by insulin. Pretreatment of synstatin also inhibited the insulin-stimulated ALP activity. Taken together, these results suggest that insulin stimulates the association of insulin receptor with syndecan-1 and the complex formation of syndecan-1 and integrin could play an important role in ERK I/II-ALP signaling pathway in osteoblast cells.