The C,N co-doped TiO₂ photocatalyst was prepared by interacting the chicken egg white having various weights (1, 2, and 4g) with 1g of TiO₂ in an autoclave through the hydrothermal process at 150°C. The C,N co-doped TiO₂ photocatalysts were characterized using Fourier transform infrared (FTIR), X-ray diffraction (XRD), specular reflectance UV/visible (SRUV/Vis), and transmission electron microscope (TEM) instruments. The photocatalytic activity of the co-doped TiO₂ was evaluated by monitoring the photo-decolorization of Congo red dye under visible light through a batch experiment. The characterization results assigned that the C and N atoms from the chicken egg white have been successfully co-doped into TiO₂ through interstitial and substitutional combination, which could notably narrow their band gap energy entering into the visible region. In line with the gap narrowing, the co-doping C,N into TiO₂ could remarkably improve the photocatalytic activity under visible light in the dye photo-decolorization. The enhancement of the photocatalyst activity of TiO₂-C,N was controlled by the weight of the egg white introduced, and 2g of the egg white resulted in the highest activity. Further, the best dye photo-decolorization, which was about 98, of 10mg/L Congo red dye in 100mL of the solution under visible irradiation could be reached by applying TiO₂-C,N prepared from 2g of the egg white, within 45min, at pH 7, and 50mg of the photocatalyst mass.