Abstract: A method of manufacturing a curved structural element made of composite material has a complex, open cross-section the structural element is formed by the assembly of components made of composite material. A plurality of flat, fresh components are prepared, each component being constituted by a flat layer of curved fibres previously infused with resin, combined with a pre-impregnated layer with straight fibres. Hot-forming of the flat, raw components is then performed. The hot-formed, fresh components are then assembled in accordance with a predetermined sequence on a polymerization tool. The tool includes a shaped, inflatable device astride which a C-shaped raw component is deposited. Finally, the fresh components assembled on the tool are subjected to a polymerization cycle in an autoclave. The inflatable device is inflated by the pressure produced in the autoclave to apply a predetermined pressure from the inside of the C-shaped fresh component.