NOVELTY - Dry-type alumina microparticles have BET specific surface area (S') of 10-50 m2/g. The number of hydroxyl groups contained in the surface of dry-type alumina microparticles is 20 or less per nm2 . The light absorbency ( tau ) of a water suspension containing 0.2 wt.% dry-type alumina microparticles with respect to light having wavelength of 700 nm satisfies a specific relation (I).    USE - Dry-type alumina microparticles are used in alumina-containing resin binder dispersion liquid used for forming inorganic particle layer of separator (all claimed) used in lithium-ion secondary battery. Can also be used as abrasives, sintered compact material, heat-resistant filler of resin, raw material for single crystals, filler for abrasion-resistance, cosmetics, accurate resin molded product filler, filler for dentistry materials, toner external addition material, etc.    ADVANTAGE - The dry-type alumina microparticles have excellent monodispersibility, and reduced coarse particle content and number of hydroxyl groups in the surface, and provide separator having thin inorganic particle layer with excellent strength, electrolyte solution permeability, reliability, and heat resistance. The raise of viscosity in the dispersion liquid is suppressed.    DETAILED DESCRIPTION - Dry-type alumina microparticles have BET specific surface area (S') of 10-50 m2/g. The number of hydroxyl groups contained in the surface of dry-type alumina microparticles is 20 or less per nm2 . The light absorbency ( tau ) of a water suspension containing 0.2 wt.% dry-type alumina microparticles with respect to light having wavelength of 700 nm satisfies the relation: ( tau ) less than or equal to 170S'-1.4-0.1 (I). INDEPENDENT CLAIMS are included for the following:    (1) manufacture of dry-type alumina microparticles, which involves producing spherical alumina microparticles from gaseous aluminum compound as raw material using a flame formed using gaseous aluminum compound, oxygen, and combustible gas at adiabatic flame temperature of 2500 K or more in the presence of outermost loop introduction gas. The ratio of amount (mol/hour) of combustible gas required with respect to sum of amount (mol/hour) of combustible gas supplied from a burner and raw material reacted completely during the manufacturing process is 5 or more. The ratio of outermost loop introduction gas volume (Nm3/hour) per 1 kg of generated alumina is 1-5. The outermost loop introduction gas is a mixed gas of inert gas e.g. oxygen and nitrogen;    (2) preservation of dry-type alumina microparticles, which involves accommodating the dry-type alumina microparticles in a packaging bag made from sheet having an oxygen permeability of 10 L/m2.day.atmosphere or less at 25 degrees C and a water vapor transmission rate of 50 g/m2.24 hours or less;    (3) alumina-containing resin binder dispersion liquid, which contains more than 30 vol.% dry-type alumina microparticles. The viscosity of the dispersion liquid is 20 Pa.second or less; and    (4) separator, which consists of an inorganic particle layer formed by coating the alumina-containing resin binder dispersion liquid on the surface of a microporous resin film.