A structure for the transport, installation and dismantlement of a deck (2) of a fixed oil platform (1) for maritime use, the structure including a floating U-shaped hull (11) fitted with at least three lifting legs (12) adapted so as to rest upon the bottom of the sea, each lifting leg (12) being associated with mechanical displacement units (20), and a shuttle (30) which can be displaced along the lifting legs (12) by the hull (11) and which is applied to the lower surface of the deck (2) in a support position for the deck, the shuttle (30) being provided with locks (36, 37) for locking on the lifting legs (12). A method for the transport, installation and dismantlement of a deck of a fixed oil platform is also disclosed.