Polarization of $τ$ lepton from scalar tau decay as a probe of neutralino mixing

The $\tau$ lepton arising from the scalar tau ($\st$) decay is naturally polarized. $\ptau$ depends on the left--right mixing of the $\st$ and the gaugino--higgsino mixing of the neutralino. The polarization $\ptau$ could be measured from the energy distribution of the decay products of $\tau$ at future $\epem$ colliders. A measurement of $\ptau$and of the $\st$ production cross section allows to determine both these mixing angles.