Gas-phase resistances to the vaporization of three mercury halides into atmosphere at elevated temperatures were evaluated. Lab-scale vaporization experiments for mercuric bromide, mercuric iodide and mercuric chloride were per-formed and the results were analyzed to evaluate gas-phase resistance to vaporization of three mercuric halides using the vaporization and condensation model. Overall mass transfer coefficients, K_G, for the sample mercuric halides, were in the range between 4.8×10^-6 g-mole sec^-1 cm^-2 atm^-1 at the temperatures from the subliming to boiling tem-peratures and were much smaller than interfacial mass transfer coefficients, k_i. It was estimated that resistance of pure gas-phase mass transfer is much larger than that of the phase transition between condensed and gas phases. It could be there-fore said that gas-phase mass transfer coefficients, k_G for mercuric halides, were nearly equal to overall mass transfer coef-ficient, K_G which could be determined as a function of temperatures.