In this research, polyaniline–titanium dioxide (PANI/TiO₂) nanocomposite thin films were effectively synthesized and evaluated for their carbon monoxide (CO) gas sensing capabilities. Titanium isopropoxide was used as a precursor to prepare TiO₂ nanoparticles via the sol–gel method, while polyaniline (PANI) was synthesized through chemical oxidative polymerization. The PANI/TiO₂ nanocomposite was obtained by blending both components in m-cresol and spin-coating the resulting mixture onto glass substrates. The structural, optical, and thermal properties of the prepared materials were characterized using X-ray diffraction (XRD), Fouriertransform infrared spectroscopy (FTIR), UV–Visible spectroscopy, and thermogravimetric analysis (TGA). XRD confirmed the formation of anatasephase TiO₂ and revealed a reduced crystallite size in the composite (25 nm) compared to pure TiO₂ (30 nm), indicating polymer–oxide interaction and suppressed grain growth. FTIR and UV–Vis spectra confirmed strong interfacial bonding and charge transfer between PANI and TiO₂, enhancing visible-light absorption and stability. The PANI/TiO₂ sensor showed a rapid and reversible response to CO concentrations (0–1000 ppb), exhibiting high linearity (R² = 0.901) and a detection limit of 0.40 ppb. These findings suggest that the PANI/TiO₂ nanocomposite is a promising, cost-effective, and highly sensitive material for CO detection in environmental and industrial applications.