Calcineurin dephosphorylated microtubule‐associated protein 2 (MAP2) and τ factor phosphorylated by cyclic AMP‐dependent and Ca²⁺, calmodulin‐dependent protein kinases from the brain. Tubulin, only phosphorylated by the Ca²⁺, calmodulin‐dependent protein kinase, served as substrate for calcineurin. The concentrations of calmodulin required to give half‐maximal activation of calcineurin were 21 and 16 nM with MAP2 and τ factor as substrates, respectively. The K_m and V_maxvalues were in ranges of 1–3 μM and 0.4–1.7 μmol/mg/ min, respectively, for MAP2 and τ factor. The K_m value for tubulin was in a similar range, but the V_max value was lower. The peptide map analysis revealed that calcineurin dephosphorylated MAP2 and τ factor universally, but not in a site‐specific manner. The autophosphorylated Ca²⁺, calmodulin‐dependent protein kinase was not dephosphorylated by calcineurin. These results suggest that calcineurin plays an important role in the functions of microtubules via dephosphorylation.