In this work, carbon nano-tube/TiO2 (CNTs/TiO2) nanocomposites were prepared using a conventional sol-gel method. To further obtain a uniform catalyst film, chitosan (CS) was used as a crosslinker for the CNTs/TiO2 composite. The structure and property of CNTs/TiO2/CS film were characterized using XRD, FT-IR, TEM, SEM, and UV-vis. The photocatalytic activities of CNTs/TiO2/CS film were measured through the photocatalytic degradation of gaseous formaldehyde. Compared with the commercial TiO2, higher degradation was achieved with the CNTs/TiO2/CS film due to stronger absorbability and synergetic effect among CNTs, TiO2, and CS.