Niobium (Nb) was successfully doped into zinc oxide (ZnO) thin film via a modified sol–gel spin coating technique. Zinc acetate, diethanolamine, and isopropyl were used as starting material, stabilizer, and solvent, respectively. Energy Dispersive X-ray Spectroscopy (EDX) analysis shows the presence of Niobium of 1.01 at. %. on ZnO thin films. Field Emission Scanning Electron Microscopy (FESEM) shows the thin film composed of nanoparticles. The estimation size of particles slightly reduced from 44.15 nm for undoped ZnO nanoparticles to 35.77 nm after the introduction of the niobium dopant. The roughness of Nb-doped ZnO thin films was lower as compared to undoped films based on atomic force microscopy (AFM) analysis. The optical properties were investigated using UV–vis and the results had shown that both samples exhibit good transmittance in visible range. In addition, the absorption edge was red-shifted after being doped with niobium. The estimated optical band gap of Nb-doped ZnO reduced to 3.27 eV from 3.30 eV for undoped ZnO nanoparticles.