  The rare decays of $\Lambda_b$ baryon governed by the quark level transitions
$ b \to s$, are investigated in the fourth quark generation model popularly
known as SM4. Recently it has been shown that SM4, which is a very simple
extension of the standard model, can successfully explain several anomalies
observed in the CP violation parameters of $B$ and $B_s$ mesons. We find that
in this model due to the additional contributions coming from the heavy $t'$
quark in the loop, the branching ratios and other observables in rare
$\Lambda_b$ decays deviate significantly from their SM values. Some of these
modes are within the reach of LHCb experiment and search for such channels are
strongly argued.
