Fourth-generation effect onCPviolation inB→Kφdecays

CP-violating asymmetries in the B→Kφ decays are studied in the four-generation model. The absorptive part in the penguin amplitude leads to the CP-violating asymmetry in the $B_U^{\pm }$→$K^{\pm }$φ decays, which could be as large as ±15% in the four-generation model, although it is at most a few percent in the three-generation model. The asymmetry between the $B_d^0$→$K_S^0$φ and B${¯}_d^0$→$K_S^0$φ decays is also expected to be ±10% on Υ(4S) through the penguin absorptive part with the contribution of the fourth-generation quark.