Asymmetric synthesis of (R)-cyanohydrins from aldehydes and hydrogen cyanide using (R)-oxynitrilase from almond in micro-aqueous phase was studied by GC chiral analysis. Reaction time, content of acetic acid, reaction medium, water activity, reaction temperature and substrate structure all had remarkable effects on the reaction. (R)-oxynitrilase from almond accommodates a wide variety of aromatic, heterocyclic and aliphatic aldehydes. Benzaldehyde was found to be the best substrate for the (R)-oxynitrilase from almond. At low temperature 0～5℃,both conversion rate and enantiomeric excess of the product were above 99%.