Light pipe technology gives an effective way to transmit sunlight into room. It is much better as an auxiliary lighting method in buildings that are short of daylight. Photocatalytic oxidation is an emerging technology for destruction of dilute air contaminants that is currently under commercial development, which using TiO2 as photocatalyst. Light pipe combined with photocatalysis technology will bring not only good luminous environment but also better indoor air quality. Light pipe combined with photocatalysis to decompose formaldehyde under sunny conditions in summer was tested in Beijing. The light pipe is a straight light pipe, which is 550mm long, with diameters of 280mmm.Degussa P25 titanium dioxide (“Degussa”, Germany) as photocatalyst was coated on the surface of the emitter of the light pipe. The experiment shows obvious effect on decomposing formaldehyde under sunny conditions. The intensity of sunlight nearly has little effect on the photocatalytic decomposition under sunny conditions.