Bismuth–lithium alloys are considered primary candidates for the reductive extraction step in the on-line reprocessing of molten salt reactor fuel. The corrosion behavior of molybdenum-based alloys and Hastelloy® B-3 alloy (taken for comparison) was examined here in a liquid Bi–Li (5 mol.%) alloy at 650 °C. MoW10, MoW30, and TZM corrosion-resistant alloys were studied as prospective construction materials for holding liquid bismuth–lithium alloy. Rates of corrosion were determined by the gravimetric method as well as by chemical analysis of corrosion products formed in liquid-phase Bi–Li alloy. The microstructure and chemical composition of samples of the materials and Bi–Li alloys containing the corrosion products after the tests were determined using inductively coupled plasma–atomic emission spectroscopy, X-ray fluorescence analysis, scanning electron microscopy, and energy dispersive spectroscopy. TZM molybdenum-based alloy corrodes in the bismuth-lithium alloy due to the formation of a zirconium–bismuth intermetallic compound, which passes into the liquid phase. The corrosion rates of MoW10, MoW30, and TZM alloys at 650 °C were 16, 16, and 23 µm/year, respectively. Hastelloy® B-3 alloy, despite its high molybdenum content, was subjected to severe corrosion in liquid Bi–Li alloys due to dissolution of nickel in liquid bismuth. The corrosion rate of this alloy was 14 mm/year.