The present invention relates to an inorganic oxide powder which is suitably used to form an inorganic oxide porous film having excellent heat resistance, insulation properties and film strength, regardless of a small basis weight, and also having porosity capable of imparting sufficient ion permeability on at least one surface of a positive electrode, a negative electrode, or a separator that constitutes a nonaqueous electrolyte secondary battery. Disclosed is an inorganic oxide powder, wherein: 1) an average three-dimensional particle unevenness is 3.6 or more, and 2) an abundance ratio in number of particles having a particle diameter of less than 0.3 μm is 50% or more.