Synthesis method of fine and pure AlN powder from Al powder by means of floating-type fluidized-bed was investigated. Concentration of oxygen and water vapor in reacting nitrogen was carefully controlled in. the range 4 to 600 ppm. Ultrapure Al powder as a raw material was continuously fed into nitrogen stream with a flow rate of 1.6 cm/s from the end of the reactor, and was nitrided, at 1550 degreesC. AN powders which were nitrided in nitrogen containing oxygen and/or water vapor in the range 50 to 100 ppm, were considered to be suitable for fabrication of high thermal conductive ceramics, because the resulting AN powders were perfectly nitrided and the color of them was pure white indicating the powders being ultrapure. The amounts of impurities such as metals and oxygen context in the powders were extremely low. The powders were composed of primary particles with 0.1 to 0.2 mm in size and specific surface areas of them were 10.0 m(2)/g. The formation process of the fine AlN powder was presumed to be constituted of several elementary reaction steps involving explosive and combustive nitridation of Al particles. The AN powder had good sinterability, and high thermal conductive AlN ceramics with value of 255 W/mK could be obtained by sintering at 1900 degreesC for 32 hours in a nitrogen with aid of 3wt% to 5 wt% Y2O3. Neither pore nor precipitation of the second phase was observed at the gram boundary, and then the extensive gram growth was observed.