3-[2-Cyclopropyl-4-(4-fluorophenyl)-3-quinolyl]prop-2-enenitrile is prepared by reacting 2-cyclopropyl-4- (4-fluorophenyl)quinoline-3-carbaldehyde with acetonitrile in the presence of a base and then adding a dehydrating agent to the reaction mixture to conduct dehydration. Under ordinary conditions, novel 3-[2-cyclopropyl-4-(4-fluorophenyl)-quinolin-3-yl]-3-hydroxypropionitrile is formed as an intermediate in the above reaction. Incidentally, when the above reaction is conducted in an organic solvent, 3-[2- cyclopropyl-4-(4-fluorophenyl)-3-quinolyl]prop-2-enenitrile is directly formed.