  We examine the rare decays $B_s\to l^+l^-$ and $B\to Kl^+l^-$ in the
framework of the topcolor-assisted technicolor ($TC2$) model. The contributions
of the new particles predicted by this model to these rare decay processes are
evaluated. We find that the values of their branching ratios are larger than
the standard model predictions by one order of magnitude in wide range of the
parameter space. The longitudinal polarization asymmetry of leptons in $B_s \to
l^+l^-$ can approach $\ord(10^{-2})$. The forward-backward asymmetry of leptons
in $B \to Kl^+l^-$ is not large enough to be measured in future experiments. We
also give some discussions about the branching ratios and the asymmetry
observables related to these rare decay processes in the littlest Higgs model
with T-parity.

High Energy Physics - Phenomenology