Stathmin (oncoprotein 18, op18) is a ubiquitous cytosolic phosphoprotein with various regulatory functions in cell proliferation, differentiation signaling, and activation. In particular, stathmin is involved in the regulation of tubulin dynamics through inhibition of microtubule formation and/or microtubule depolymerization. Stathmin interacts with soulable tubulins (a, b-tubulin) resulting in the formation of T2S complex which sequesters free tubulin, impeding tubulin formation. Stathmin activity is regulated through phosphorylation at Ser16, Ser25, Ser38 and Ser63 by various protein kinases (e.g. MAP-kinase, p34cdc2 kinase), weakening stathmins affinity to tubulin. A mutation on stathmin can lead to excess build up of mitotic spindle and with possible consequence of unregulated cell cycles seen in cancer cells. Stathmin is also known as the generic member of a protein family which includes neural proteins SCG10, SCLIP and RB3/RB3'/RB3". All members in this family exhibits tubulin binding ability.