Boehmite (aluminum oxyhydroxide, BE) selectively adsorbs phosphate ion. Recently, we studied the recovery efficiency of phosphate ion and the adsorption/desorption mechanism by calcining the BE surface in the temperature range of 200∼1150°C. As a result, the amount of phosphate ion adsorbed/desorbed by BE at a calcining temperature of 400∼700°C exhibited a higher value than the BE at other calcining temperatures, and the recovery efficiency of the phosphate ion was 90% or higher. On the other hand, the amount of phosphate ion adsorbed/desorbed onto BE at a calcining temperature of 1100°C or higher exhibited a lower value than the BE before calcining. Based on the phosphate ion adsorption/desorption behavior results, and the XRD and FT-IR results, it was determined that when the calcined BE is suspended in water, water molecules are dissociated, producing hydroxyl groups on the surface, and these hydroxyl groups exchange ions with the phosphate ion, thus the amount of phosphate adsorbed ion reaches a maximum. The phosphate ion adsorbed by BE was adsorbed by a sodium hydroxide solution, just like the BE before calcination. It became evident that by calcining BE, it is possible to obtain an adsorbent with a high phosphate ion recovery efficiency. [DOI: 10.1380/ejssnt.2005.63]