Disclosed herein is a floating structure with a fuel gas tank for storing gas fuel to be fed to a dual fuel propulsion system under a cabin area. According to the present invention, there is provided a floating structure with a fuel gas tank storing gaseous fuel used as fuel while floating at sea, including: a cabin area disposed on an upper deck of the floating structure; a fuel gas tank mounted under the cabin area in the hull of the floating structure; and a blocking member mounted between the cabin area and the fuel gas tank to secure safety of the cabin area.