Photocatalytic oxidation is an emerging technology for destruction of dilute air contaminants that is currently under commercial development, which using TiO2 as photocatalyst. UV illumination of the TiO2 film placed in a gaseous formaldehyde (HCHO) / air container resulted in the total degradation of formaldehyde to CO2 and H2O. Despite its potential advantages, the key unresolved issues in the commercial application of photocatalytic oxidation technologies to contaminated air purification are that of optimum photocatalytic reactor design and the load of photocatalyst. In this paper, successive alternating banks of UV lamps and structured catalyst support monoliths are mounted directly in a square duct. The photocatalyst TiO2 was loaded on the surface of honeycomb monoliths by different methods. The square duct including banks of UV lamps and structured catalyst support monoliths was put in a 4 cubic meters glass container. The polluted gas was injected into the container. The photocatalytic degradation of air contaminants was studied. The results shown that the air contaminants formaldehyde can be degraded by photocatalytic oxidation technology. The photocatalytic efficiency was different photo-initiated by UV lamps with peak wavelength at 254 nm and 365 nm. The distance between the UV lamps bank and the honeycombs monoliths was found to affect the efficient of photodegradation.