An investigation was performed, using the slow strain-rate tensile test technique, to determine whether nickel and typical nickel base alloys were susceptible to embrittlement by liquid mercury at room temperature. The alloys Monel 400, Monel R405, Monel K500, Inconel 625, Inconel 718, and Inconel X750 displayed intergranular embrittlement to different degrees. Nickel 200 and Inconel 600 had transgranular breaks. The alloys Incoloy 800 and Incoloy 825 were not embrittled under these test conditions, giving cup and cone fractures, but some surface cracking did arise in the necked region. The fracture mode was governed by the strain at which cracking initiated with lower values favoring integranular separations. Some alloys showed a progression from intergranular to transgranular to microvoid coalescence fractures across the cross section, the latter failures occurring at higher strain levels. The relative embrittlement of the alloys did not correlate with the mechanical properties or the stacking fault energies, but is perhaps related to composition, for the alloys higher in iron content were affected less.