One of the most significant methods in water and waste water treatment and decreasing their contaminants is photocatalytic degradation by semiconductors. This technique is a new, effective, rapid and destructive method to achieve this purpose. While TiO 2 is one the most remarkable photocatalysts, g-C 3 N 4 is a new material that has grabbed interest in recent years. The g-C 3 N 4 has outstanding features such as optical, mechanical, electrical and thermal property. Therefore, the aim of this study is synthesis of TiO 2 -CNT and g-C 3 N 4 , doping of metal elements and assessment of decolorization property of these components. TiO 2 was synthesized by titanium isopropoxide precursor. In order to crystalize initial amorphous Titania and obtain desired crystalline phase, heating treatment has been used. The synthesized materials were characterized by EDX, FESEM, XRD, FTIR methods. The results of FESEM image confirmed the presence of layer of coated TiO 2 with 30-50 nm thickness on CNT with 10-30 nm diameter has dispersed efficiently. Furthermore, image of g-C 3 N 4 showed that g-C 3 N 4 is formed in a layered structure. The result of XRD indicated that crystalline TiO 2 in all synthesized materials, after heating treatment, was anatas and also presence of two important carbon nitride strips that is indication of carbon nitride layers formation, has been seen. In addition, the FTIR confirmed the presence of Ti-O bonding, which is indication of TiO 2 formation, and also there was also a C-N bonds indicating the formation of carbon nitride plates. In order to investigate the photocatalytic function of TiO 2 , CNT with carbon nitride and metal elements, methylene blue at a low concentration in the water phase was used as a model for organic pollutants in the wastewater. The results of this study showed that, the photocatalysts containing zinc has the best results in most cases. Moreover, the color removing by photocatalysts in an alkaline environment is much better than the acid and neutral environment. As the amount of photocatalyst is greater, the level of active photocatalyst sites is higher and the results are better. Finally, the tests were replicated three times and the results were roughly similar and result of decolorization was approximately 87 % in average.