Thermal stability of carbonic anhydrase (CA) immobilized within polyurethane (PU) foam was investigated. The catalytic activity of the enzyme was estimated by using p-nitrophenyl acetate (p-NPA) as the substrate in tris buffer containing 10% acetonitrile. The immobilized CA was stable during the repeatable washings and stability tests over 45 days stored in tris buffer at ambient conditions indicating that the CA was covalently attached to the polyurethane (PU) foam by crosslinking. The immobilized CA was found to he 98% stable below 50 degrees C, whereas a drastic decrease was seen at temperatures between 50 and 60 degrees C. The optimum temperature for the immobilized CA was found to be 45 degrees C and it lost its activity completely at 60 degrees C. Thermal deactivation energies for the free and immobilized CA were estimated to be 29 and 86 kcal/mol, respectively. The association of unfolded CA with the polymeric backbone chains of the PU foam was also addressed. It was concluded that the immobilized CA was highly stable at temperatures less than 50 degrees C and could be used in biomimetic CO2 sequestration processes. (C) 2010 American Institute of Chemical Engineers Biotechnol. Prog., 26: 1474-1480, 2010