Abstract: A filtration device is provided, configured to be assembled between a tube seat and an air diffuser of a ventilation system, including: a main body, at least one filter and at least one light source. The main body includes an air inlet connected with the tube seat, an air outlet connected with the air diffuser and a shielding portion blocking between the air inlet and the air outlet. The shielding portion defines at least one passage. The at least one filter is disposed on the main body and corresponds to the at least one passage. The at least one filter has a photocatalyst material disposed thereon. An illumination area of the at least one light source corresponds to the at least one passage. A distance between the at least one light source and the at least one filter is smaller than or equal to 100 mm.