AMP-activated protein kinase ( AMPK) is an energy-sensing Ser/Thr protein kinase originally shown to be regulated by AMP(1). AMPK is activated by various cellular stresses that inhibit ATP production or stimulate ATP consumption(2). In addition to its role in metabolism, AMPK has recently been reported to reshape cells by regulating cell polarity and division(3-6). However, the downstream targets of AMPK that participate in these functions have not been fully identified. Here, we show that phosphorylation of the microtubule plus end protein CLIP-170 by AMPK is required for microtubule dynamics and the regulation of directional cell migration. Both inhibition of AMPK and expression of a non-phosphorylatable CLIP-170 mutant resulted in prolonged and enhanced accumulation of CLIP-170 at microtubule tips, and slower tubulin polymerization. Furthermore, inhibition of AMPK impaired microtubule stabilization and perturbed directional cell migration. All of these phenotypes were rescued by expression of a phosphomimetic CLIP-170 mutant. Our results demonstrate, therefore, that AMPK controls basic cellular functions by regulating microtubule dynamics through CLIP-170 phosphorylation.