Fatigue strength of adhesive bonded box beams with longitudinal partition was investigate. From results of the fatigue tests, it was seen that the fatigue strength of bonded beams was higher than that of spot welded beams. Fatigue strength of bonded beams was independent of plate thickness and partition. The flexural rigidity of the box beams in the plane of partition can increase without decrease of torsional rigidity and torsional fatigue strength, if the partition is jointed by adhesive bonding instead of spot welding.Since the fatigue strength and rigidity of adhesive bonded joints can be higher than the spot welded joints in the weight saving structures, it is expected that the structural adhesive joints will be employed more in the automobile body structure.- For assuring the introduction of this joint more into the automobile body structures, it is necessary that the fatigue tests on the modelmembers of the actual members used in the automobile body structure in addition to those of the simple joints such as tension shear and T-type tension - are conducted and the property of the fatigue strength on the adhesive bonded members is known. But, we now have little data on fatigue tests of the adhesive bonded members.In the present research to be reported, the fatigue tests on adhesive bonded box beams with a longitudinal partition under torsion, which are typical members in automobile body structure, were carried out and the effects of the presence of partition and plate thickness on fatigue strength were investigated. Comparing the results of fatigue tests on adhesive bonded box beams with those on spot welded box beams used at present in automobile body structure, the property of fatigue strength on these adhesive bonded box beams was cleared.