This paper presents the experimental study of cryogenic two-phase thermosyphons with nitrogen, artificial air (79% N2 + 21% O2) and ambient air as working fluids for the basic thermal performance characteristic. The thermosyphon is made of stainless steel, 36.8 × 10-2 m long with an inner diameter of 0.9 × 10-2 m. The axial temperature distribution as a function of heat transfer rate and critical heat transfer rate are measured for various filling ratios under the operating vapor pressure of about 0.1 MPa. The experimental results indicate that there is very little qualitative difference in the heat transfer characteristics among the three kinds of working fluid, though nitrogen is superior to both kinds of air. In case of nitrogen, the effective thermal conductivity of the thermosyphon is found to be about 20 times as large as that of copper at 80 K. However, for both kinds of air, they are about 14 times as large as copper. The maximum heat transfer rates, about 93 W for nitrogen and about 73 W for both kinds of air, are roughly the same values as that of a freon thermosyphon at normal ambient temperature. The results of ambient air thermosyphon, as well as nitrogen one, demonstrate the applicability as the working fluid for a cryogenic two-phase thermosyphon.