Abstract: An improved temperature-sensing tube for an aquarium, includes a temperature-sensing tube, one end of a temperature sensitive switch made from two metal sheets if welded to a heat-sinking piece, the main body of the heat-sinking piece is formed coincident with the shape of and is completely kept close to the inner wall of the outer pipe. Abnormal temperature generated by the running of related members in the electric circuit board is transmitted to the heat sink. Thus, the whole temperature-sensing device can be more accurate and reliable with more economical cost.