  We investigate the semileptonic and leptonic B decays, B to D^{(*)} tau nu
and B to tau nu in our multi-Higgs-doublet models, while keeping in mind the
enhancement of the top forward-backward (FB) asymmetry (A^t_{FB}) at the
Tevatron. In these models, the extra (pseudo)scalar bosons contribute to
A^t_{FB} with large flavor-changing Yukawa couplings involving the top quark,
but the contribution of the charged Higgs boson to A^t_{FB} is negligible.
However, it may significantly affect B decays: especially, B to D^{(*)} tau nu
and B to tau nu. We investigate the constraints on the B decays, based on the
recent results in BaBar and Belle experiments, and discuss the possibility that
the allowed parameter region in the B decays can achieve large A^t_{FB}.
