A non-destructive assessment of phase transformation and residual stress is presented for a 3 mol.% Y2O3 added ZrO2 ceramic using Raman microprobe spectroscopy. Low CIP pressure has been selected in the sample procedure to increase a potential to transform ZrO2. Aging tests were made and the transformation depth and residual stresses caused by transformation were evaluated by Raman spectroscopy A Raman microprobe technique using a visible wavelength laser coupled with a confocal optical device may enable one to retrieve spatially resolved information along the material subsurface. To demonstrate the potentiality of the confocal technique, aging of a ZrO2 sample has been made in autoclave and phase transformation gradually promoted from the surface towards the sub-surface of the sample (up to ～60 µm, in a sample autoclaved 168 h). Then, a quantitative spatially resolved assessment was attempted on these samples from their surface. The confocal information from the subsurface was compared with results of Raman spectroscopy collected from a cross-section. Accordingly, a quantitative equation was proposed, which allows the quantitative assessment of the thickness of the surface layer, which underwent phase transformation in ZrO2 ceramics, according to in-depth non-destructive assessments.