A dual online liquid chromatography device according to an embodiment of the present invention comprises: a first pump for injecting a first solvent or a mixed solution containing the first solvent and a second solvent; a second pump for injecting the first solvent or the mixed solution containing the first and second solvents; a specimen intake valve connected to the first pump and a specimen injector for injecting a specimen; a column selection valve connected to the second pump and the specimen intake valve; and a dual column valve including a plurality of ports, one side of which is connected to the column selection valve and an opposite side of which is connected to a first column and a second column.