  In this article, we assume the two nonets of scalar mesons below and above 1
GeV are all $\bar{q}q$ states, and study the semi-leptonic decays $B\to
S\ell^-\bar{\nu}_{\ell}$, $B\to S\ell^+\ell^-$ and $B\to S\bar{\nu}\nu$ both in
the standard model and in the universal extra dimension model using the $B-S$
form-factors calculated by the light-cone QCD sum rules in our previous work.
We obtain the partial decay widths and decay widths, which can be confronted
with the experimental data in the future to examine the natures of the scalar
mesons and constrain the basic parameter in the universal extra dimension
model, the compactification scale $1/R$.
