Abstract: This invention relates to a novel self-closing fire rated floor door. More particularly, this invention pertains to a novel floor door which uses fusible plugs and compressed gas cylinders for automatically closing the floor door when ambient temperature rises above a predetermined temperature, due to a fire. A self-closing fire rated floor door assembly comprising: (a) a fire rated frame with an opening therethrough; (b) a fire rated door hingedly connected to the frame and cooperating with the opening; (c) a fluid cylinder which is pivotally connected to the frame and the door, the cylinder when pressurized with fluid opening the door relative to the frame, and when depressurized, closing the door relative to the frame; (d) a fusible plug, rated according to a specific temperature, connected in fluid-tight manner with the fluid cylinder.