For effective regeneration of the adsorbent used in a desiccant humidity conditioner, the possibility of rnicrowave irradiation for desorption of water from zeolite was studied. To investigate the effect of microwave irradiation on the water desorption rate from zeolite (0.69 mm), experiments were conducted in a N-2 flow type adsorption column equipped with a microwave irradiator. Desorption of water from zeolite by microwave heating under conditions of N-2 gas of 30 degrees C with relative humidity 40%, gas flow rate of 0.053 m/s and microwave power of 200-800 W was compared with that for hot-air heating at 47 degrees C. The following results were obtained. (1) The amount of water desorbed from zeolite was 1.6-2.0 times larger by microwave heating than by hotair heating. This amount corresponded to that obtained by hot-air heating at 10-16 degrees C higher than the zeolite bed temperature. It was found that the desorption amount with microwave irradiation was larger than that with hotair heating, regardless of microwave power. (2) Maximum desorption rate was about 5 times faster by microwave heating at 800 W than that by hot-air heating. (3) Desorption rate with microwave irradiation increased with microwave power, and it decreased linearly with the increase in water adsorption ratio in zeolite.