The photocatalytic oxidative decomposition of gaseous acetaldehyde (AcH) in air under visible light irradiation (wavelength >400 nm) was driven by bismuth tungstate (Bi2WO6) polycrystalline particles with a hierarchical structure, flake-hall particles, prepared by hydrothermal reaction at various temperatures. Complete decomposition of AcH into CO2 was proven for all of the flake-ball particle photocatalysts. The rate of CO2 liberation was increased in proportional to the specific surface area for flake-ball particles with similar high deuces of crystallinity. Kinetic analysis assuming Langmuirian adsorption of AcH revealed that the initial rate of photocatalytic decomposition could be reproduced by first-order kinetics with respect to the amount of surface-adsorbed AcH. A linear relationship between the photocatalytic activity and surface area of photocatalysts under conditions in which other physical properties such as the photoabsorption property, crystalline content, exposed crystal facets, and secondary particle size are almost the same was experimentally revealed.