The alumina layer growth in thermal barrier coatings (TBC) was investigated by impedance spectroscopy. The oxide layer growth was monitored nondestructively through modulus spectrum measurement. The TBCs investigated consists of the top coat yttria stabilized zirconia (YSZ) and the bond coat. A frequency response analyzer coupled with dielectric interface was used for impedance measurement. The results depicted efficient separation of electrical responses from different oxide layers in TBCs.