Durability in the ocean environment is one of the most important problems to be considered, in designing offshore structures. One solution of the problem has found in using concrete. The advantage of concrete structure is its corrosion resistance. However, the structure has disadvantages in heavy structural weight and long building time. The concepts of steel/concrete hybrid and assembling precasted blocks are thought to make up for these weak points of concrete structures. In this paper, the longitudinal strength of steel/prestressed concrete hybrid barge is dealt with, experimentally. The test model, about 1/4 in scale, was produced by assembling three precasted blocks and prestressing in the longitudinal direction. Three points bending test was performed on the model. The test results showed that the structure has enough strength for bending moment, but has narrow margin of cracking due to shear force in the towing condition.