  Form factors parameterizing the semileptonic decay $B_{c}\rightarrow
D_{s}^{\ast}l^{+}l^{-}$ ($l=\mu ,\tau $) are calculated using the frame work of
Ward Identities. These form factors are then used to calculate the physical
observables like branching ratio and helicity fractions of final state
$D_{s}^{\ast}$ meson in these decay modes. The analysis is then extended to the
the universal extra dimension (UED) model where the dependence of above
mentioned physical variables to the compactification radius R, the only unknown
parameter in UED model, is studied. It is shown that the helicity fractions of
$D_{s}^{\ast}$ are quite sensitive to the UED model especially when have muons
as the final state lepton. Therefore, these can serve as a useful tool to
establish new physics predicted by the UED model.

High Energy Physics - Phenomenology