To provide a method for synthesizing 2,2'-bis(trifluoromethyl)-4,4'- biphenylcarboxylic acid at a low cost without using a special equipment.

This synthesis method comprises the following steps: reacting 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl with a nitrous acid compound in an acid catalyst to form a diazonium salt; reacting the diazonium salt with iodine and/or an iodine compound to form 2,2'-bis(trifluoromethyl)-4,4'- diiodobiphenyl; reacting the diiodobiphenyl compound with copper (I) cyanide to form 2,2'-bis(trifluoromethyl)-4,4'-dicyanobiphenyl; and hydrolyzing the reaction product.