-Alumina powder of fine particles having the primary particle diameters of from 10 nm to 100 nm, and of a high ratio of -phase and further having capability to provide a sintered body with high density, and a method of manufacturing the -alumina powder is provided. The method for manufacturing the -alumina powder comprises a step of mixing an aluminum compound which is the precursor for the corresponding -alumina and at least one selected from the group consisting of a titanium compound, an iron compound, a chromium compound, and -alumina, and aluminum nitride, aluminum carbide and a aluminum boride as a seed crystal(s), and a step of calcining the mixture at a temperature of from 600 C. to 1000 C. in the presence of HCl gas in an concentration of 1% by volume to 20% by volume.