Titanium dioxide nanoparticles were functionalized with maleic anhydride. The chemical stability of the modified samples was tested by ultrasonic and magnetic stirring. The effectiveness of these treatments was confirmed by Total Organic Carbon (TOC) and Thermo Gravimetric Analysis (TGA). Fourier Transform Infrared Spectroscopy (FTIR) and UV-Vis Diffuse Reflectance Spectroscopy (DRS) results clearly showed the chemical anchored maleic anhydride on the titanium dioxide surface as a bidentate bridging adsorption. The surface modification of titanium dioxide extended its light absorption range to the visible light region. X-Ray Diffraction (XRD) patterns did not show any change in the crystal structure of the modified samples with respect to pristine titanium dioxide. The quantification of chemically adsorbed maleic anhydride and the reaction efficiency were calculated from data obtained by Differential Thermal Analysis (DTA) and TGA. The photocatalytic activity was analyzed by degrading methyl orange. The kinetic reaction was better using the functionalized titanium dioxide.