Measurement of electroencephalogram (EEG) requires accurate estimation of tissue conductivity. Among the head tissues, skull compartment has less conductivity due to compacta and spongiosa, which impacts on EEG measurement. Therefore, skull conductivity plays a vital role in head modeling, forward computation and source localization. In this study, we have investigated the effects of scalp potentials due to skull conductivity perturbations in realistic head models using different skull to brain and/or scalp conductivity ratio (σ _ratio). Several studies used this σ _ratio as 1/80, however, other studies found the values of σ _ratio between 1/20 and 1/72. Each head model constructed from the values of different σ _ratio ranging from 1/20 to 1/72 is compared to the head model constructed from σ _ratio = 1/80. The obtained results demonstrated that the skull conductivity perturbations have effects on EEG and the head model constructed from less σ _ratio generates larger errors due to higher potential differences.