2D TiO₂ thin films and 3D flower-like TiO₂-based nanostructures, also decorated with SnO₂, were prepared by chemical and thermal oxidation of Ti substrates, respectively. The crystal structure, morphology and gas sensing properties of the TiO₂-based sensing materials were investigated. 2D TiO₂ thin films crystallized mainly in the form of rutile, while the flower-like 3D nanostructures as anatase. The sensor based on the 2D TiO₂ showed the best performance for H₂ detection, while the flower-like 3D nanostructures exhibited enhanced selectivity to CO(CH₃)₂ after sensitization by SnO₂ nanoparticles. The sensor response time was of the order of several seconds. Their fast response, high sensitivity to selected gas species, improved selectivity and stability suggest that the SnO₂-decorated flower-like 3D nanostructures are a promising material for application as an acetone sensor.