Abstract: An extensible metallic tube structure has a big hollow tube, an engaging head, a small hollow tube, a locating column, an O-shaped ring, a washer, a C-shaped fixing device, and a controlling sleeve. The big hollow tube having an inwardly indented groove at the upper periphery is engaged with the engaging head at one end. The small hollow tube fixed with locating column is led through the other end of the big hollow tube. In sequence, the O-shaped ring, the washer, the C-shaped fixing device and the controlling sleeve are led through the upper end of the small hollow tube. The controlling sleeve is screwed up to the engaging head via threads. An inner protruding flange defining the other side of the inwardly indented groove of the big hollow tube will prevent the small hollow tube from coming off when it being extended to the extreme.