Luminescence spectra of Pb(1-x)Cd(x)I2 mixed crystals have been investigated under optical excitation at various energies around the absorption edge. The free exciton luminescence of PbI2 is replaced by a broad emission band at the concentration x around 0.03-0.05. The emission is attributed to inhomogeneously broadened luminescence of excitons localized by the fluctuating potential of the disordered alloy. An anomalous shift of exciton transition energy is observed between x = 0.03 and 0.05, which is discussed in relation to the exciton Bohr radius.