This present invention concerns a mold for the aluminothermic welding of railway rails. The compressible lining (58) used to seal the molding die in relation to leakages of the weld metal in the liquid state is limited to the parts of the contact surfaces (52) of the parts (19) of the mold on the rails to be welded, corresponding to the bottom, the sides and the top of the foot, to the sides of the web and below the head. The rigid refractory material of the parts (19) is exposed in the parts (67, 71) of the contact surfaces corresponding to the sides and the top of the head, and suitable to be removed selectively from the latter. This makes it easy to adapt the mold to rails with different degrees of wear.