  We study the spin properties of top quarks produced in collisions of
polarized photons in the threshold region. For a relatively heavy top quark the
influence of non-perturbative effects is small and its polarization parameters
can be predicted in perturbative QCD. The measurements of the top polarization
may allow a novel test of QCD in the $t\bar{t}$ system. In particular, they may
provide a new way to determine the precise value of $\alpha_s$ and to study the
properties of the top quark.
