The invention provides novel 3α-hydroxysteroid dehydrogenase mutants, sequences that code for these enzyme mutants, methods for producing the enzyme mutants, and the use thereof in enzymatic reactions of cholic acid compounds, and in particular in the production of ursodeoxycholic acid (UDCA). The invention further provides processes for the synthesis of UDCA using the enzyme mutants and the production of UDCA using recombinant microorganisms that have been subjected to multiple modifications.