In conjunction with structural design of cast-in-situ diaphragm R/C walls constructed at underground and along the periphery of buildings, biaxial bending-shear tests of R/C wall specimen were performed. During the tests, the loads out of plane applied perpendicular to the wall surface which represent earth pressure soon, were kept constants, the loads in plane parallel to the wall surface which represent shear force due to seismic load were applied to it's failure. Influence of the load out of plane on failure mode, deflection and strength is discussed in this paper. Comparing with specimens subjected to loads in plane only, the following facts were observed from the test results. (A) When the applied constant load out of plane was less than about 50% of the calculated load carring capacity in it's direction, 1. in all the specimens failed in plane, their failure modes, shear failure, flexural failure and flexural-shear failure, were not so much influenced by the presence of the load out of plane. 2. strength and rigidity of shear failured specimens were not influencd by the load out of plane. 3. non-dimensional interaction curve between strength in plane and strength out of plane was almost circular arc when failed in flexure or in flexure-shear. (B) When the applied constant load out of plane was greater than about 50% of the calculated load carring capacity in it's direction, 1. all the specimens failed in shear out of plane and strength in plane decreased greatly. 2. the rigidity of the specimen supposed to fail in shear when subjected to the load in plane only was not effected by the presence of load out of plane. On the contrary, due to the presence of load out of plane, the reduction of the rigidity of the specimen supposed to fail in flexure or in flexure-shear when subjected to the load in plane only began at 2/3〜1/3 of the maximum load and the ductility decreased to 1/3〜1/8.