A flameproof rayon fiber having excellent flameproofness as well as excellent flame retardance, a method for manufacturing the same, and a flameproof fiber structure are provided. The flameproof rayon fiber according to the present invention includes components of silicon and sodium. Glass remains when the fiber is burned at 800°C, the glass component has a property of softening at 800°C, and when subjected to an X-ray fluorescence analysis, the rayon fiber has a silicon content in the range of 5 to 30% by mass and a sodium content in the range of 0.1 to 3% by mass. The flameproof rayon fiber according to the present invention can be manufactured by preparing an undiluted viscose solution; adding a solution containing a silicate compound containing an alkali metal to the undiluted viscose solution so as to make an alkali metal-containing silicate compound-added viscose solution; performing spinning by extruding the alkali metal-containing silicate compound-added viscose solution through a spinneret into a spinbath containing sulfuric acid, thus producing a fiber to be treated containing the silicate compound; and treating, in a scouring or aftertreatment process, the fiber to be treated with a solution having a pH in the range of 4 to 11 and a buffer action and containing sodium. A flameproof fiber structure of the present invention contains at least 30% by mass of the flameproof rayon fiber.