Abstract: A study on eddy current testing of stainless steel tubes with ribs in the inner wall was addressed. A feed-through coil had been used to separate the heterotypic stainless steel tubes with artificial flaws made by EDM, from the normal ones by the analysis of impedance plane diagram and the data processing. The results revealed that the feed-through coil could inspect the artificial circumferential groove of 0.20 mm in depth at the optimum testing frequency. At the same time, the signal of the circumferential groove and the signal of the heterotypic parts, the inner rib of width 10 mm, of the tubes could be separated, leading to a reliable result.