The enantioselectivity of serine proteases in the transesterification of N‐acetyl‐(D,L)‐ phenylalanine esters with propan‐1‐ol in cyclohexane is strongly influenced by the leaving ability of the alcoholate group. Moreover the enantioselectivity is greatly influenced by the addition of small amounts (0.33 M) of organic additives. Addenda with a small molecular volume like e.g. ethanol and acetonitrile increase the rate for the L‐enantiomer whereas alcohols with bulky alkyl groups like e.g. tert‐butanol and 2‐methylbutan‐2‐ol enhance the activity of the enzyme towards the D‐enantiomer. This enables a rational tuning of the enantioselectivity as was demonstrated for four different proteases (α‐chymotrypsin, subtilisin Carlsberg, Aspergillus oryzae protease, and elastase).