  We investigate the leading effects of extending the Standard Model of
electroweak interactions by an extra iso-singlet up- and down- type quark pair
on various distributions and total branching ratio of the inclusive B-> X_s l^+
l^- (l =e,\mu) rare B decays. The presence of the extra vector-like down quark
$D$ results in the non-unitarity of the extended quark mixing matrix V, which
in turn leads to b-> s FCNC at the tree level proportional to (V^\dagger
V)_{sb}. On the other hand, the effective penguin and box vertex functions are
sensitive to the mass of the extra iso-singlet up quark m_U. The experimental
upper bound on BR(B-> X_s \mu^+ \mu^-) is used to constrain the parameters of
the model. It is shown that the shapes of the differential branching ratio and
forward-backward asymmetry distribution are very sensitive to the value of the
model parameters. We also calculate the CP aymmetry distribution of the
dileptonic decay in the vector-like quark model. It is shown that, for a
typical choice of the model parameters, asymmetries up to around 10% can be
achieved for certain values of the dilepton invariant mass.
