The invention concerns a mold for aluminothermal welding of railway tracks. The refractory coating (58) used for sealing the molding cavity (25) against liquid-phase welding metal leakage extends continuously from one to the other of the surface portions (52) defining spans supporting the parts (19) of the mold on the rails (2) to be welded, and delimits itself the molding cavity (25), thereby providing better continuity between the weld seam and the rails (2) and a better surface condition of the weld seam, as well as enhancement of preheating performance.