Abstract: Carbonic anhydrase Ⅸ (CA Ⅸ), which is one of carbonic anhydrases (CAs), is a tumor-associated transmembrane protein. CA Ⅸ is detected in various solid tumors, but little or not in the normal tissues; it catalyzes a reversible conversion of carbon dioxide to bicarbonate and proton, controlling pH of intracellular and extracellular space and maintaining the acid-base balance of tissues in favor of tumor growth and invasion. CA Ⅸ is clearly an attractive target for anti-tumor drugs and also as a prognostic factor of patients in the diagnosis and treatment of tumors. CA Ⅸ inhibitors can be used as diagnostic drugs for molecular imaging of tumors and also be used as antitumor drugs for blocking the CA Ⅸ mediated pathway. Molecular imaging using ⁸⁹Zr, ¹¹¹In, ¹²⁴I or ¹²⁵I labeled monoclonal antibodies targeting CA Ⅸ can precisely position the distribution and sensitively detect expression of CA Ⅸ. In radioimmunotherapy experiments at maximum tolerated dose, tumor growth was effectively delayed by monoclonal antibodies targeting CA Ⅸ labeled with ⁹⁰Y, ¹³¹I, ¹⁷⁷Lu or ¹⁸⁶Re. This review focused on the presentation of CA Ⅸ and its applications in the nuclear medicine research.