An NAD-dependent secondary alcohol dehydrogenase (ADH) produced by Rhodococcus sp. GK1 was purified about fivefold with a yield of 82% by hydrophobic interaction chromatography. This enzyme reduced monoketones, diketones and α-dicarbonyl compounds; it oxidized secondary alcohols but not primary alcohols. Optimum pH was 7.0 or 8.5 for reduction or oxidation of substrates, respectively, and optimal temperature for activity was 55 °C. The apparent molecular mass of ADH was about 60 kDa by gel filtration chromatography.