  The ${\Upsilon}(1S)$ ${\to}$ $B_{c}D_{s}^{\ast}$ weak decay is studied with
the perturbative QCD approach firstly. It is found that (1) main contributions
to branching ratio come from the longitudinal and parallel helicity amplitudes,
(2) branching ratio, longitudinal and parallel polarization fractions are
sensitive to the wave functions of the ${\Upsilon}(1S)$ meson, (3) branching
ratio for the ${\Upsilon}(1S)$ ${\to}$ $B_{c}D_{s}^{\ast}$ decay can reach up
to $10^{-9}$, which might be promisingly measured by the future experiments.
