A process for producing a 2-oxobicyclo[3.1.0]hex-3-ene-6-carboxylic acid derivative represented by the formula (I) (wherein R1 represents hydrogen, C¿1-6? alkyl, C3-6 cycloalkyl, C1-6 alkyl substituted by C3-6 cycloalkyl, C1-6 alkyl substituted by optionally substituted phenyl, C1-6 alkyl substituted by C1-6 alkoxy, C1-6 hydroxyalkyl, C1-6 alkyl substituted by C1-6 alkylthio, C1-6 mercaptoalkyl, or optionally substituted phenyl), characterized by reacting a 4-hydroxy-2-oxobicyclo[3.1.0]hexane-6-carboxylic acid derivative represented by the formula (II) (wherein R?1¿ is the same as defined above; and R2 represents hydrogen or a hydroxyl-protecting group) in the presence of an acid or base. Also provided is a process for producing a compound useful in the efficient synthesis of a 2-amino-3-fluorobicyclo[3.1.0]hexane-2,6-dicarboxylic acid derivative.