20α-Hydroxysteroid dehydrogenase (20α-HSD), which catalyzes the conversion of progesterone to its inactive form 20α-dihydroprogesterone, is expressed in murine placenta and has been suggested to play roles in maintaining pregnancy. To understand the role of 20α-HSD during pregnancy in the goat, as a first step, cloning and sequencing of 20α-HSD cDNA were performed. The full nucleotide sequence of 20α-HSD cDNA was determined on samples obtained from the corpus luteum at the luteal phase of the estrous cycle and the placenta in late pregnancy by RT-PCR and 3' and 5' RACE systems. Cloned 20α-HSD cDNA consisted of 1124 bp and belonged to the aldo-keto reductase superfamily. From the start codon to stop codon there were 323 amino acids, the same as in other species. To verify whether the protein derived from goat 20α-HSD cDNA had 20α-HSD activity, the cDNA was expressed by bacteria. Bacterially expressed goat 20α-HSD protein showed 20α-HSD enzyme activity. A tissue distribution study demonstrated that 20α-HSD was expressed in the placenta, but not in the adrenal gland, liver and spleen during pregnancy. The present study suggests that goat 20α-HSD is another member of the aldo-keto reductase superfamily and that it plays a role in the placenta during pregnancy.