Astaxanthin (AXT) 3,3'-dihydroxy-beta,beta-carotene-4,4'-dione, from the group of carotenoid, specifically as xanthophyll, is investigated in this work on its polymorphism. The method to obtain a second polymorph of AXT is described. Polymorph I can be purchased as a commercial product or obtained via phase transformation from polymorph II. Polymorph II can be prepared from polymorph I by a thermal treatment carried out in a differential scanning calorimetry (DSC). The resulting crystals are characterized by different analytical techniques. X-ray powder diffractometer (XRPD) and resonance Raman spectroscopy prove the existence of two different crystalline polymorphs. Simultaneous thermal analysis (STA) gives additional information on their thermal behaviors. Polymorph I melts at 230 degrees C and polymorph II melts at 216 degrees C. Phase transition experiment carried out by slurry conversion experiment reveals two polymorphs are monotropically related. Polymorph II is the metastable form. (C) 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.