Abstract: In this work, two types of carbonic anhydrase were found in the crude extracts of Anabaena sp.strain PCC7120.In high CO2-grown cells, c.a.85% total CA activity was inhibited by 35μmol/L EZ, and its half inhibited concentration (I50) was 7.4μmol/L; With the elevation of EZ levels, the second peak of inhibition for CA appeared when the concentration of EZ reached 150μmol/ L.The remaining 15% CA activity was completely inhibited in the presence of 250μmol/L EZ, and its I50 was 190μmoI/L.In air-grown cells of Anabaena sp.PCC7120, the similar two peaks of inhibition for CA also appeared: the low I50 was 6μmol/L and the high I50 was 120μmol/L.Isolation of carboxysomes and the assays in vitro showed, that only one inhibition peak for CA appeared in the preparations of carboxysomes.As expected, the overall CA activity was inhibited in the presence of 35μmol/L EZ, with I50 of 5.2μmol/L, which was very similar to the low I50 value in the crude extracts of air-grown cells and high CO2-grown cells.The results indicated that low levels of EZ specifically inhibited the CA located within carboxysomes.The other types of CA, which had a high I50 (120 - 190μmol/L) and contained c.a.15-20% of the total CA activity of the crude extracts, probably located in the cell membrane.