The present invention is to enhance the stability and enzyme activity of an L-arabitol dehydrogenase derived from Neurospora crassa using techniques from quantum mechanics and molecular mechanics and partial mutation techniques. More specifically, the present invention relates to a method for preparing an L-arabitol dehydrogenase in which a residue which affects enzyme stability is found through a screening based on quantum mechanics and molecular mechanics, and enzyme activity is enhanced by mutation of the found residue, nucleic acid molecules encoding the L-arabitol dehydrogenase, a vector including the nucleic acid molecules, a transformant including the vector, a mutant of the L-arabitol dehydrogenase and an improved L-arabitol dehydrogenase.