The MmsB gene product from Bacillus cereus ATCC14579 exhibits 3-hydroxypropionate dehydrogenase activity. It encodes the 32-kDa enzyme protein composed of 292 amino acids. Recombinant 3-hydroxyisobutyrate dehydrogenase (3-HIBADH) was purified 100-fold from cell extract by ammonium sulfate fractionation and column chromatography. The enzyme catalyzed oxidation of 3-hydroxypropionate (3-HP) between pH 7.0 and 10.0 with optimal activity between 8.8 and 9.0. A Km of 16.8 mM for 3-HP was calculated from a Lineweaver-Burk plot. The semialdehyde as products has been proven by spectrophotometric determination. The dehydrogenase apparently has no metal ion requirement. Kinetic determinations established that 3-HIBADH was more active with NADP(+) than NAD(+), which did not show similarity with previously reported 3-HIBADH except that from Thermus thermophilus.