  In a scenario in which fourth generation fermions exist, we study effects of
new physics on the differential decay width, forward-backward asymmetry
$A_{\text{FB}}$ and integrated branching ratio for $B\to X_s \ell^+ \ell^-$
decay with $(\ell=e,\mu)$. Prediction of the new physics on the mentioned
quantities essentially differs from the Standard Model results, in certain
regions of the parameter space, enhancement of new physics on the above
mentioned physical quantities can yield values as large as two times of the SM
predictions, whence present limits of experimental measurements of branching
ratio is spanned, contraints of the new physics can be extracted.
  For the fourth generation CKM factor $V_{t^\prime b}^\ast V_{t^\prime s}$ we
use $\pm 10^{-2}$ and $\pm 10^{-3}$ ranges, take into consideration the
possibility of a complex phase where it may bring sizable contributions,
obtained no significant dependency on the imaginary part of the new CKM factor.
  For the above mentioned quantities with a new family, deviations from the SM
are promising, can be used as a probe of new physics.
