Using the responsible form factors calculated via full QCD, we analyze the $Lambda_{b}rightarrow Lambda ell^{+}ell^{-}$ transition in the standard model containing fourth generation quarks (SM4). We discuss effects of the presence of $t$ fourth family quark on related observables like branching ratio, forward-backward asymmetry, baryon polarization as well as double lepton polarization asymmetries. We also compare our results with those obtained in the SM as well as with predictions of the SM4 but using form factors calculated within heavy quark effective theory. The obtained results on branching ratio indicate that the $Lambda_{b}rightarrow Lambda ell^{+}ell^{-}$ transition is more probable in full QCD comparing to the heavy quark effective theory. It is also shown that the results on all considered observables in SM4 deviate considerably from the SM predictions when $m_{t}geq 400 GeV$.
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