Carbonic anhydrase plays different roles in various tissues. It is a key enzyme that regulates the acid-base homeostasis under both normal and pathological conditions. In this study, carbonic anhydrase (CA; E.C 220.127.116.11) was purified from erythrocytes of Van cat (Fells catus) by affinity chromatography. The purification rate was found to be 367.21-fold. SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis) was used to control the purity of enzyme. Optimal pH, ionic strength, and temperature for enzyme activity were determined. Molecular weight of CA was identified to be about 30 kDa by SDS-PAGE. Optimal pH and temperature were 8.0 and 40 degrees C. The highest activity was found at a concentration of 0.12 M (NH4)(2)SO4 as ionic strength.