A 5-fluorooxindole-3-carboxylic acid ester represented by a formula (2): ##STR00001## wherein R.sup.1 is a group selected from the group consisting of an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms, an unsubstituted or substituted cycloalkyl group having 3 to 7 carbon atoms, an aralkyl group having 7 to 10 carbon atoms or an aryl group having 6 to 14 carbon atoms.