Aluminum nitride (AlN) ceramics are commonly used as high thermal conductive ceramics. Their thermal conductivity is strongly dependent on the chemical state of the starting powder surfaces. Control of the powder surfaces is important. For this purpose, the powder surface characteristics must be studied. Conventional chemical analytical methods do not provide enough information on the surface characteristics which may influence the sinterability and thermal conductivity of the products. In this work, temperature programed desorption (TPD) analysis was used to investigate the difference of the surface characteristics of powders produced by nitridation of aluminum (powder A), CVD (powder B) and carbothermal reduction (powder C). Powder surfaces of α-Al2O3, γ-Al2O3 and θ-Al2O3 were also investigated to evaluate the desorption mechanism of H2O molecules on the AlN powder surfaces. The following conclusions are obtained. First of all, desorptions of H2, NH3, H2O and mass 28 molecules are observed from the AlN powder surfaces. An interesting conclusion which explains the difference between the most popular commercial AlN powder used to obtain the high thermal conductivity and the other commercial powders, is obtained by the TPD spectra. Desorption of NH3 molecules is observed only for powder A and powder B. Tendency of H2O desorption for powder C is similar to that of θ-Al2O3. This implies that powder C has a similar surface as θ-Al2O3.