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We examine the conductometric CO sensing of TiO 2 nanoparticle films prepared with a recently developed flame technique. Porous films of crystalline TiO 2 nanoparticles were grown directly on interdigitated electrodes by repeatedly translating electrodes over a premixed stagnation flame doped with titanium tetraisopropoxide as the titanium precursor. Flame-deposited electrodes with particle diameter around 9 nm show enhanced sensitivity to CO by up to an order of magnitude compared to sensing films prepared using a commercial TiO 2 powder with the particle diameter around 25 nm. A gas-surface model is used to examine chemical kinetic and equilibrium behaviors and explain the sensor responses. The analysis shows that the nature of the gas-surface reactions is similar between these films. The desirable feature of flame-deposited sensing film is attributed to the smaller particle size which provides a greater surface area and a more electrically sensitive conduit.