Blends of polystyrene (PS) and esterified starch has been prepared using an epoxy functionalized PS as compatibilizer along with zinc stearate as prooxidant. The starch phthalate (Stph) loading was varied from 20 to 60%. The mechanical, thermal, and biodegradability studies of the blends were carried out as per the ASTM standards and the results were compared with that of neat PS. The blends exhibited enhanced mechanical properties with the addition of compatibilizer although the biodegradation rate slows down. The blend containing 40% starch ester with 12% compatibilizer showed maximum tensile strength. Thermogravimetric and differential scanning colorimetric analyses has been done for the blends, and the neat PS and the glass transition temperature of the blend has been obtained at 327 K. The water absorbency of the blends showed an increase with the increase in loading of Stph and a reduction with the addition of compatibilizer. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012