  The collider experiments at the Tevatron and the LHC provide us the
possibility of probing the existence of a light charged Higgs boson. In this
paper we study semi-leptonic decay of a polarized top quark via the charged
Higgs boson ($t(\uparrow)\to H^{+}b \to l^{+}\nu_{l}b$). It is shown that the
asymmetry or spin correlation coefficient of the charged lepton depends on the
$\tan\beta$ and $M_{H^{\pm}}$ and is quite different from the Standard Model.
This sensitivity of asymmetry to $\tan\beta$ and $M_{H^{\pm}}$ could be
utilized in the experimental searches for the light charged Higgs for
separation of the signal from backgrounds in the $t\bar{t}\to
H^{+}W^{-}b\bar{b}\to\tau^{+}\nu_{\tau}\l^{-}\bar{\nu_{\l}}b\bar{b}$ (and vice
versa). It might be useful for obtaining better bounds in the
($\tan\beta,M_{H^{\pm}}$) plane too.
