Caveolae, discovered by electron microscope in the 1950s, are membrane invaginations that accommodate various molecules that are involved in cellular signaling. Caveolin, a major protein component of caveolae identified in 1990s, has been known to inhibit the function of multiple caveolar proteins, such as kinases, which are involved in cell growth and proliferation, and thus considered to be a general growth signal inhibitor. Recent studies using transgenic mouse models have suggested that insulin signal may be exempted from this inhibition, which rather requires the presence of caveolin for proper signaling. Caveolin may stabilize insulin receptor protein or directly stimulate insulin receptors. Other studies have demonstrated that caveolae provide the TC10 complex with cellular microdomains for glucose transportation through Glut4. These findings suggest that caveolin plays an important role in insulin signal to maintain glucose metabolism in intact animals. However, the role of caveolin in insulin signal may differ from that in other transmembrane receptor signals.