<p>Bismuth oxide (Bi₂O₂) nanoparticles have been doped with nickel (Ni) and graphene oxide (GO), acting as an efficient humidity sensor. Humidity sensors based on nanomaterials were found to be efficient in measuring and controlling humidity. Different nanostructured materials, including bare Bi₂O₂, Bi₂O₂-doped GO, Bi₂O₂-doped Ni, and Bi₂O₂-Ni-doped GO, have been synthesized through the co-precipitation method. The synthesized structure was identified and characterized through different characterization techniques, including X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), mapping analysis, Fourier Transform Infrared Spectroscopy (FTIR), and Ultraviolet–Visible Spectroscopy (UV–Vis). The average crystallite sizes as estimated from XRD were found to be 47.34 nm, 26.9 nm, 19.3 nm, and 17.5 nm for Bi₂O₂, Bi₂O₂-doped GO, Bi₂O₂-doped Ni, and Bi₂O₂-Ni-doped GO, respectively. The EDX mapping has confirmed the uniform distribution of the building elements within the matrix of the synthesized materials. The optical study revealed that the optical absorbance and the band gap energy of the Bi₂O₂ nanoparticles were changed by adding Ni and GO to the matrix. The rGO has reduced the bandgap of the Bi₂O₂ from 2.64 to 2.39 eV, while the addition of Ni to the Bi₂O₂ raised the bandgap value to 3.45 eV, which slightly decreased to 3.39 eV after adding rGO to the Bi–Ni oxide composite. The humidity-sensing behavior was explored for all synthesized structures in a range of relative humidity from 11 to 97%. Among all investigated materials, Bi₂O₂-doped Ni revealed the lowest value of sensitivity, while Bi₂O₂-Ni-doped GO attained the highest value of sensitivity within the investigated range. The Nyquist plot was developed for studying the humidity-sensing behavior of the investigated samples.</p>