Formaldehyde in the indoor environment may be degraded using nano-particulate titanium dioxide (TiO₂) photocatalysis to improve air quality. In the work described, a polytetrafluoroethylene filter is employed as the substrate for a nano-particulate TiO₂ coating. This is mounted in an experimental setup developed for the tests, similar to an actual air purification system, which are conducted at room temperature. The effects on the formaldehyde photocatalytic degradation rate of some key factors are investigated, including initial concentration, stream flow rate, reaction temperature, light source intensity, and relative humidity. Within the experimental ranges studied, the degradation rate increases with the enhancement of initial concentration and light intensity. The stream flow rate and reaction temperature have dual effects on the degradation rate. It is shown that the degradation rate is relatively high under low relative humidity.