A new type of steel seawall, comprised of steel pipe piles reinforced with truss members and double straight sheet pile walls aligned in arc-shape, has been proposed. It is expected to be economical due to its structural rationality. The horizontal resistance of the structure was investigated by a model test, where a one-tenth scale-down model placed in earth tank was loaded horizontally. The test yields the following results;
　When lateral load is applied to this type of the structure, the pull-out resistance of piles reaches to maximum, then the piles under the ground reach their yield strength at almost maximum resistant point. It does not show a brittle behavior and the load decrease after the maximum is rather mild.
　The truss structure with an upper horizontal member and a diagonal bracing have very high shear rigidity compared with that of sand filled in between double sheet pile walls, and the trusstransfer the load from the back to the front wall and piles effectively.
　The embedded portion, though relatively shallow, of the arc-shaped sheet piles in the front row makes a large contribution to the high horizontal resistance of the structure.
　A 2-D analytical model to predict the structural behavior of the structure is proposed in consideration of the test results. The simulative calculation results by the model yield good agreement with the test results.