Stathmin is a regulator of microtubule dynamics which undergoes extensive phosphorylation during the cell cycle as well as in response to various extracellular factors. Four serine residues are targets for protein kinases: Ser‐25 and Ser‐38 for proline‐directed kinases such as mitogen‐activated protein kinase and cyclin‐dependent protein kinase, and Ser‐16 and Ser‐63 for cAMP‐dependent protein kinase. We studied the effect of phosphorylation on the microtubule‐destabilizing activity of stathmin and on its interaction with tubulin in vitro. We show that triple phosphorylation on Ser‐16, Ser‐25, and Ser‐38 efficiently inhibits its activity and prevents its binding to tubulin.