The present invention relates to a process for preparing β-ketonitriles of the general formula I in which R1 is, inter alia, C1-C12-alkyl, C2-C12-alkenyl, C2-C12-alkinyl, C3-C8-cycloalkyl, C3-C8-cycloalkyl-C1-C4-alkyl, phenyl-C1-C4-alkyl, phenoxy-C1-C4-alkyl or benzyloxy-C1-C4-alkyl; R2 is, inter alia, hydrogen, C1-C12-alkyl, C2-C12-alkenyl, C2-C12-alkinyl, C3-C8-cycloalkyl, C3-C8-cycloalkyl-C1-C4-alkyl, phenyl, phenyl-C1-C4-alkyl, phenoxy-C1-C4-alkyl or benzyloxy-C1-C4-alkyl, which comprises reacting a nitrile of the formula II in which R1 has one of the meanings given above with a carboxylic ester of the formula III in which R2 has one of the meanings given above and R3 is C1-C12-alkyl, C1-C4-alkoxy-C1-C4-alkyl, C3-C8-cycloalkyl, C3-C8-cycloalkyl-C1-C4-alkyl, phenyl-C1-C4-alkyl, phenoxy-C1-C4-alkyl or benzyloxy-C1-C4-alkyl, where the reaction is carried out in the presence of a potassium alkoxide and at least 80% of the nitrile of the formula II are added to the reaction under reaction conditions.