The B -> X(s)l(+)l(-) and B -> Xs gamma decays with the fourth generation

If the fourth generation fermions exist, the new quarks could influence the branching ratios of the decays of B --> X(s)gamma and B --> X(s)l(+)l(-). We obtain two solutions of the fourth generation CKM factor V-t'*V-s(t'b) f rom the decay of B --> X(s)gamma. We use these two solutions to calculate t he new contributions of the fourth generation quark to Wilson coefficients of the decay of B --> X(s)l(+)l(-). The branching ratio and the forward-bac kward asymmetry of the decay of B --> X(s)l(+)l(-) in the two cases are cal culated. Our results are quite different from that of SM in one case, almos t the same in another case. If Nature chooses the former, the B meson decay s could provide a possible test of the fourth generation existence.