3-Isopropylmalate dehydrogenase (IPMDH) from the psychrotrophic bacterium Vibrio sp. I5 has been expressed in Escherichia coli and purified. This cold adapted enzyme is highly homologous with IPMDHs from other organisms, including mesophilic E. coli and thermophilic T. thermophilus bacteria. Its molecular properties are similar to these counterparts. While the E. coli and T. thermophilus enzymes are hardly active at room temperature, the Vibrio IPMDH has reasonable activity below room temperature. The thermal stabilities, conformational flexibilities (H/D exchange) and kinetic parameters of these enzymes were compared. The temperature dependence of the catalytic parameters of the three enzymes, show similar but shifted profiles. The Vibrio IPMDH is a “much better enzyme” at 25°C than its counterparts. With decreasing temperature i.e. with decreasing conformational flexibility, the specific activity reduces also, however, in the case of the Vibrio enzyme, the residual activity is still high enough for normal physiological operation of the organism. The cold-adaptation strategy in this case is achieved by creation of an extremely efficient enzyme, which has reduced but still sufficient activity at low temperature.