Toluidine blue-carboxymethyl chitosan-carbon nanotubes composite photosensitizer was obtained by reflux method,the carbon nanotubes were modified by carboxymethyl chitosan, and the surface of the carbon nanotubes modified with carboxymethyl chitosan was further prepared by the reflu x method.The stability and dispersibility of carbon nanotubes modified by carbox ymethyl chitosan and the effect of carbon nanotube diameter on the spectral properties of composite photosensitizer are st udied.The morphology and optical properties of the composite photosensitizer were characterized by transmission e lectron microscopy (TEM), infrared (IR) absorption spectroscopy and visible light absorption spectroscopy. The dispersibility and stability of the photosensitizer were observed by experiments.The results show that the toluidine blue was better compounded to the carbon nanotubes,which was modificated using carboxyme thyl chitosan.The carbon nanotubes diameter has little influence on the synthesi s of the compound photosensitizer,but the one with small radius is easy to agglo merate in water,and the compound has a good dispersity in aqueous solution.Its visible light absorption peak is located at 611nm.This study will provide an i mportant experimental basis for biomedical applications.