The invention discloses a method for preparing R-
mandelic acid by the aid of two-step
microbial transformation processes. The method includes carrying out transformation reaction on ethyl benzoylformate, first thalli and
buffer solution with a pH (potential of
hydrogen) value of 6-8 under conditions of the temperature of 20-45 DEG C and the speed of 100-200 rpm to obtain R-ethyl mandelate; carrying out reaction on the R-ethyl mandelate, second thalli, organic solvents and
buffer solution with a pH value of 7-9 under conditions of the temperature of 20-40 DEG C and the speed of 100-200 rpm to obtain the R-
mandelic acid. The ethyl benzoylformate is used as a substrate during the transformation reaction, the first thalli are obtained by means of
fermentation cultivation by the aid of
saccharomyces cerevisiae and are used as catalysts during the transformation reaction, and the
buffer solution with the pH value of 6-8 is used as a reaction medium during the transformation reaction. The R-ethyl mandelate is used as a substrate during the reaction, the second thalli are obtained by means of
fermentation cultivation by the aid of
bacillus cereus and are used as catalysts during the reaction, the organic solvents are used as complex solubilizers during the reaction, and the buffer solution with the pH value of 7-9 is used as a reaction medium during the reaction. The method has the advantages that the method is low in cost and is
environmentally friendly, and the
reaction conditions are mild; the R-
mandelic acid is easy to industrially produce on a large scale; the method is easy and convenient to implement and high in
molar transformation rate; the yield can be increased and can reach 99.8%, and the ee value can be increased and can reach 100%.