TiO2 nanowires (NWs) have been synthesized by thermal evaporation process, using the vapor-liquid-solid (VLS) growth mechanism and Au thin film as a catalyst which was deposited on titanium/quartz substrates. Optical and microstructure characteristics of TiO2 NWs have been studied under different argon carrier gas flows. The gas flow was varied from 60 to 170 sccm. The results of X-ray diffraction show that TiO2 nanowires form in rutile phase and their preferred growth are in (110) direction. The field emission scanning electron microscope images indicate that with increasing gas flow, nanowires become thinner and longer. The absorbance spectrum has been obtained through using spectrophotometer and then band gap of TiO2 nanowires were calculated. According to results, the band gap has been increased due to the quantum confinement in comparison with bulk one. The band gap increased from 3.35 eV to 3.45 eV by increasing the argon flow, since the wires become thinner and longer. The Williamson-Hall method was used as the main tools for characterization of crystallite size and microstrain. Also the other microstructure characterizations have been determined by X-ray line profile analysis such as; dislocation density and texture coefficient. The crystallinity of TiO2 NWs has been improved by increasing Ar flow due to enhancement of VLS growth mechanism. (C) 2013 Elsevier B.V. All rights reserved.