This article describes about the nature of potential drops (PDs) on carbon steel (SS400) and stainless steel (SUS304). The experimental results showed the remarkable nature of potential drops on oxidized surface. Direct current PD (DCPD) technique was used to investigate the nature of potential drops on the test surfaces with probe contact time. The nature of PDs on oxidized and oxide scale free surfaces were compared for the same experimental conditions and it is easy to compare the contaminated surface with oxide scale free surface and to decide whether the surface is oxidized or clean. Oxidized test surface is considered as two layers of different resistivities. The effect of two layers on the potential drops was illuminated by electrical image method. Electrical resistivity of oxide scale was determined by DCPD technique on the basis of the two layers of different resistivities model. In an attempt to verify the accuracy and prove the validity of the proposed method, the electrical resistivity is also determined at different probe spacing and all the results are shown to be very proximate to one another.