Abstract: Austenitic boiler tubes used in power units often suffer from security problems due to accumulation of oxide scales exfoliated from the inside tube wall. In this paper, the pulsed eddy current (PEC) testing technique was presented to quantitatively measure the accumulated oxide-scale thickness. First, an open-close sensor was designed and developed. It was simple in structure and easy to use with good feasibility. Then, a PEC experimental system was established and was applied to measure the accumulated oxide-scale thickness in TP347H tube sample. Finally, experiments were conducted to study the sensor signal characteristics, influence of sensor lift-off and the effect of receiver array. Results show that: the peak value of test signals varies linearly with the accumulated oxide-scale thickness and thus it can be used to accurately quantify the accumulation thickness; the peak value decreases linearly as the sensor lift-off increases; the influence of magnetic transformation of tube wall on measurements can be eliminated by using the peak value of differential signals between array receivers. The results may provide some guidance for the thickness measurement of oxide scales accumulated in austenitic boiler tubes.