Abstract: The mechanical properties of thermit joints at low temperature are required for constructions and repairs of railway(such as Qinghai-Tibet Railway,etc.) in cold regions.A series of tensile specimens made from two types of thermit joints,whose base metal are U71Mn and U75V rail steels,are tested at low temperature.The results show that the proof strength of the two types of joints increases as the temperature decreases,while the tensile strength reduces as the decrease of temperature.The yield ratio of the two types of joints increases with the reduction of temperature.The percentage elongation and reduction of area reduce as the temperature falls down,which present deterioration in ductility of the joints.It is better to chose U71Mn steel and the corresponding weld consumables in low temperature regions for railway constructions,because they are more ductile than U75V joints.