To improve the output performance of a desiccant humidity conditioner, a hybrid type combining heat and microwave irradiation was proposed, and the effect of heat and microwave irradiation on adsorbed water-vapor desorption from zeolites was studied. Two kinds of zeolites (4A, 13X (DF-9)) with different pore distribution and water vapor equilibrium adsorption amount were used to investigate the effect of microwave irradiation on the water desorption rate. Experiments were carried out in a N(2) flow (flow rate of 1.62-6.36 m/min) type adsorption zeolite-packed column equipped with a microwave irradiator. Desorption performance of water from zeolites by microwave heating under the conditions of N(2) gas of 30 degrees C with relative humidity 40% and microwave power of 800 W was compared with that for hot-air heating at 40-80 degrees C and microwave power of 50 W. The following results were obtained. 1) The effect of microwave irradiation was found to be better than that of hot air heating for both zeolites. The amount of water desorbed from zeolite 4A, from which desorption is difficult, and from 13X (DF-9), which has a high water vapor adsorption capacity, was respectively 2.22 and 2.59 times larger by microwave irradiation than by hot air heating. This amount corresponded to that obtained by hot-air heating at 13-43 degrees C higher than the zeolite bed temperature. 2) The desorption rate increased with the increase in pore size of the zeolites. Moreover, the desorption rate from zeolite of same pore size increased with the increase in the amount adsorbed. 3) The desorption effect of microwave irradiation was confirmed from the results of the temperature rise experiments during hot air heating and during microwave irradiation. 4) The desorption ratio showed a minimum value with respect to air flow rate. 5) For the same desorbed amount, the temperature of hybrid hot air and microwave irradiation type is lower than that of hot air heating. The microwave irradiation showed the effect of a maximum 16 degrees C decrease of the heat source.