The thermal conductivities of argon, neon, and krypton in the temperature range 1500 to 5000 deg Kelvin have been deduced from the measurement of heat transfer rates from the heated gases to the end wall in the reflected shock wave. Pressures ranged from approximately 1/2 atm to 3 atm. The relationship between thermal conductivity and temperature was assumed to be of the form k = aTb. The constant “b” was determined by a best fit to the data and the constant “a” by the known values of “k” below 1500 K. The effect of density variation in the thermal boundary layer was found to be significant in reducing the data; some previous investigations have neglected this effect.