A process for producing L-aspartyl-L-phenylalanine alkyl or aryl esters wherein L-aspartic acid and L-phenylalanine which is esterified with an alkyl group having at least two carbon atoms, an aryl group or an aralkyl group, are contacted in an aqueous medium with particular microorganisms or enzyme fractions from these microorganisms and the condensed product crystallizes out due to insolubility in the aqueous medium.