Titanium dioxide (TiO2) is a widely studied semiconductor due to its chemical stability, non-toxicity, and strong photocatalytic activity. However, its wide band gap limits visible-light utilization, motivating efforts to modify its electronic structure through doping and nano structuring. The Pechini method was used to prepare carbon-doped titanium dioxide (C-TiO2). The diffraction peaks of the XRD pattern shows (101), (004) and (200) planes of tetragonal structure of TiO2 anatase. Lattice parameters, crystallite size, and micro-strain were obtained. The crystallite size decreased from 16.53 nm to 7.46 nm. Popa rules model gives anisotropic plot with different crystallite shapes. The absorption and reflectance spectra exhibited a pronounced red shift from the ultraviolet (UV) region toward the visible and near-infrared regions in the carbon-doped samples. This enhances photocatalytic activity by decreasing the band gap, which can be used in water treatment and hydrogen production and other photocatalytic applications. The estimated optical transition energy decreased from 3.13 eV to 1.25 eV. Therefore, this study aims to synthesize carbon-doped TiO2, investigate, and correlate the relation band gap and crystalline size.