We have investigated the dispersive properties of excited-doublet four-level atoms interacting with a weak probe field and an intense coupling laser field.We have derived an analytical expression of the dispersion relation for a general excited-doublet four-level atomic system sunject to a one-photon detuning.The numerical results demonstrate that for a typical rubidium D1 line configuration,due to the unequal dipole moments for the transitions of each ground state to double excited states,generally there exists no exact dark state in the system.Close to the two-photon resonance,the probe light can be absorbed or gained and propagate in the so-called superluminal form.This system may be used as an optical switch.