Heterogeneous photocatalytic oxidation (PCO) has shown to be a promising air purifying technology in outdoor conditions using TiO2 as photocatalyst activated with UV light. Also to indoor air quality more and more attention is paid because of the very important role it plays on human health, and it can be influenced by many factors like ventilation system, building materials, furniture, cooking, and outdoor pollutants. The present work addresses the indoor air purification using photocatalytic oxidation. The photocatalytic reaction setup is introduced for the assessment of the indoor air quality. A modified TiO2 that can be activated with visible light (VIS) is used as photocatalyst due to the shortage of UV light in indoor condition. One special wall paper is applied as the substrate for the coating of the photocatalyst in the present study. Nitric oxide (NO) is one typical indoor air pollutant, which is used as target pollutant for the photocatalytic oxidation with indoor concentration level. Influential parameters like initial NO concentration, flow rate, relative humidity of the experimental environment, irradiance, photocatalyst dosage that can affect the PCO are studied. Furthermore, the second part content of the present study is introduced at the end of this paper.