Optical coherence tomography (OCT) is evaluated as a promising technique for microstructure characterization of plasma-sprayed ceramic coatings. OCT combines the principles of low coherence interferometry and optical heterodyne detection to obtain both a high sensitivity to weakly backscattered light and a high axial resolution. It can be used to accurately locate interfaces where the refractive index changes abruptly within translucent materials. In the present work, OCT cross-sectional images of thin yttria-stabilized zirconia (YSZ) coatings are considered. The interferograms forming the images are analyzed individually to successfully gather information related to light penetration depth inside coatings. The interferogram analysis allows the evaluation of the refractive index of the YSZ non-transformable tetragonal phase.