Efficiency of photocatalysis depends on the surface area and materials, and we have prepared a porous ceramic substrate coated with nanosized-TiO2 for a photocatalytic air cleaner. The surface of the porous ceramic was coated with nano-sized TiO2 and total surface area of the board (30 × 30 × 1 cm) was 7,432 m2, being 14,864 m2 as the total area in the cleaner consisting of two boards and intervened black lamps. Eighty percent of 5 ppm acetaldehyde was decomposed and generated 8 ppm of carbon dioxide for 3 hours efficiently and continuously by passing through the TiO2-coated ceramic (5 × 10 × 1 cm) under black light. Particulate dioxins (40 pg/m3) and gaseous dioxins (16 pg/m3) were removed by 7.5 and 2.8 pg/m3 by passing through four TiO2-coated ceramic (30 × 30 × 2 cm) under black-light, indicating about 80% of dioxin was decomposed by the photocatalysis. This photocatalysis system was applied for inactivation of influenza aerosol. Influenza infection is spread efficiently by inhalation of aerosol-associated influenza virus. The aerosol-associated infectivity produced by nebulizer in a 754 liter cubic space was more than 10,000 plaque-forming units and was detectable for up to 30 minutes. The aerosol-associated infectivity of influenza virus was eliminated within five minutes by a photocatalytic air cleaner. The infectious aerosol-associated influenza would accumulate by the continuous production by cough and sneeze in the closed space, resulting in the efficient influenza infection. Thus a photocatalytic air cleaner efficiently decomposed organic chemicals including acetaldehyde and dioxins and inactivated aerosol-associated influenza virus infectivity.