For improving the photocatalytic activity of titanium dioxide (TiO2), the use of appropriate conjugated polymers such as poly(hexylthiophene) (P3HT) to form composites with TiO2 can extend the absorption for the light harvesting. Such photocatalytic materials also have a high charge separation ability, which increases the photocatalytic reaction. Besides, to reduce the electron-hole recombination rates, which impact strongly the photocatalytic performance, graphene by its high electrical conductivity, can be incorporated to the P3HT/TiO2 composites in order to improve the charge transport in the materials. However, the effects of the graphene size on the photocatalytic behavior of composites have not been much studied so far. In this work, we have investigated P3HT/graphene composites and we examined the effect of the graphene size on the morphology and optical properties of the materials. Optical characterizations using, Raman, Infrared, absorption, steady and time resolved photoluminescence have been performed on composites synthesized with different graphene sizes (expressed by graphene weight per surface unit). It has been shown that their properties depend on the graphene concentration and also on its size. Based on these results and analyses, we studied the photocatalytic activities of TiO2/P3HT/graphene composite films through the degradation processes of a rhodamine solution under visible light irradiation in the presence of the composites. Highest performance was provided by composite samples containing graphene of medium size (150 m(2)/g). The improvement of photocatalytic activity of these composites is related to an increase in contact surface between graphene and polymer resulting in a better charge transfer between materials, enhancing thus their performance.