To provide a high speed twin-fuselage hydrofoil ship which has satisfactory resistant propulsive performance, sea worthiness and sea kindliness, can smoothly take-off and land from and onto water, mass-producible, and has a high strength hull structure.

Fully immersed hydrofoils 4, 5, 6 are laid in three rows between both immersed bodies 3, 3 which are supported to a deck bottom 18 of a main hull 1 on opposite sides of the latter through the intermediary of struts 2, 2, and a ridge part 19 downward projecting is longitudinally extended in the center part of the deck bottom. The rear parts of the immersed bodies re projected rearward from the struts 2, and they are tapered so that the rear edge parts thereof are gradually extended as it approaches the immersed bodies. A longitudinal wall 30 which can exhibit an effective strength is longitudinally laid between a high strength deck 151 of the main hull the deck bottom, and a crosswise wall which can exhibit an effective strength is laid between an effective deck 161 and the deck bottom, crossing the longitudinal wall between outer shell plates on opposite side walls the ship. Support members 7, 8, 9 positionally aligned with the lower end part of the longitudinal wall and suspended from the deck bottom are extended through the distal end part of the ridge part 19 so as to be secured for reinforcement, and are fixed at their lower ends to the intermediate parts of the fully immersed type hydrofoils.