  We calculate the contributions of the vector-like quark model to $\BsBs$
mixing, taking into account the constraints from the decay $B\to X_s\gamma$. In
this model the neutral bosons mediate flavor-changing interactions at the tree
level. However, $\BsBs$ mixing is dominated by contributions from the box
diagrams with the top quark and the extra up-type quark. In sizable ranges of
the model parameters, the mixing parameter $x_s$ is much different from the
standard model prediction.
