Time-Domain Optical coherence tomography is utilized as a non-contact and non-invasive method for thickness measurement. because of using broadband and low coherence light source, this method has high accuracy and axial resolution. In this paper, we will experimentally illustrate that technique of Optical coherence tomography can be used as an accurate way to measure micron thickness of transparent layer i.g. birefringent crystal of lithium niobate and polymer of PSSA.