A composite liquid agent package containing a first pouch filled with a first liquid and a second pouch filled with a second liquid; and a kit for preparing a multicomponent composition, the kit including an outer bag housing the composite liquid agent package. With an opposite end section of the first pouch and an opposite end section of the second pouch being superposed, the superposed parts are heated and pressurized to exclude sealants, which are present within the opposite end sections, outwardly of the extremities of the outer layers of the opposite end sections, while heat-fusing the two extruded sealants together to join the two pouches.