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 performed 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 for the sunple mercuric halides, were in the range between 4.8 x 10 fi and 1.6 x 10 g-mole sec cm z arm at the temperatures from the subliming to boiling temperatures and were much smaller than interfacial mass transfer wefficients, k. It was estimated that resistance of pure gasphase mass transfer is much larger than that of the phase transition between condensed and gas phases. It could be therefore said that gas-phase mass transfer coefficients, k2 which could be determined as a function of temperatures.