Recently techniques for two dimensional (2D) or three dimensional (3D) image engraving inside crystal have been developed utilizing its transparency and high refractive index. However, due to the low tolerance against shock, heaviness and high cost of crystal, poymethyl methacryslate (PMMA) can be an attractive alternative for the laser engraving because PMMA has comparable transparency and refractive index to crystal while it is much easier to process. In this paper, we present the preliminary evaluation of PMMA as laser engraving material, potentially replacing crystal. For the comparative evaluation of crystal and PMMA, we used a 3D Laser Engraving System with a Q-switched 2nd harmonic Nd:YAG laser. Pulse energy and repetition rate of Nd:YAG laser were 26.9 mJ and 50 ~ 60 Hz, respectively to produce dot engravings inside crystal and PMMA. Also, the pulse duration time was less than 10 ns. We observed the size and shape of engraved points inside both material and resulting image formation depending on the distance between points (100 ~ 150 μm) as a function of laser power output. For the surface image comparison, an optical microscopy was used, and the cross sectional views of individual points were scanned every 10 μm using an optical coherence tomography (OCT) system. Our results demonstrate that laser engraving inside PMMA created better defined image formation from pure melting process rather than from cracking process inside crystal. We also present optimal 3D laser engraving conditions for PMMA as an alternative material to improve upon crystal's disadvantages.