Carbonic anhydrase (CA) is an enzyme that rapidly catalyzes the reversible hydration of carbon dioxide (CO 2 ) in aqueous solutions. Recent progresses in CA research suggest that this biocatalyst can be used as an alternative or an additive for chemical CO 2 capture, which is considered an essential green route for the reduction of anthropogenic CO 2 emissions. However, the facilities in which CA will most likely be used usually operate under high temperature conditions, requiring a highly thermostable CA. Here, we attempted to find and characterize α-CAs originated from Persephonella marina and Thermovibrio ammonificans, thermophilic Gram-negative bacteria in deep-sea hydrothermal vents. The recombinant α-CAs expressed in Escherichia coli showed catalytic efficiencies better than the previously characterized thermophilic β- and γ-CAs from archaea, and their activities were significantly increased at higher temperatures. Remarkably, these enzymes exhibited outstanding thermostability (stable up to at least 80°C). Through long-term stability tests at 40°C and 60°C, we discovered that the novel α-CA of T. ammonificans might be the most thermostable CA ever characterized. Also, the recombinant CAs successfully accelerated CO 2 sequestration in CaCO 3 , more efficiently than mesophilic bovine CA under high temperature condition. Collectively, these results demonstrate that the α-CAs of thermophilic bacteria from deep-sea hydrothermal vents are promising biocatalysts for practical industrial CO 2 capture in terms of both activity and stability.