SnO₂ thin films were prepared by thermal chemical vapor deposition technique. The furnace temperature, deposition time and Ar flow rate were adjusted at 350ºC, 90 min and 300 sccm, respectively, whereas oxygen flow rates were varied according to preparation condition (100,150 and 200 sccm). The influence of oxygen flow rate on crystal structure, structural parameters, volumetric density, unit cell volume and electrons distribution density were deduced from the output of Rietveld refinement using Fullprof software. It was found that the crystallites size from X-ray diffraction showed synchronization with particle size from scanning electron microscopy analysis. The optical constants are greatly influenced by oxygen flow rate, where both transparency (55%-79%) and optical band gap (4.03- 4.18 eV) were increased with oxygen flow rate unlike that existed in refractive index and extinction coefficient. The catalytic performance of SnO₂ thin films was tested by the decomposition of methylene blue (MB) under UV irradiation. It was found that, the degradation rate of MB is not limited to the presence of Sn₃O₄ mixed phase, where small crystallites allowed small migration length of the photoinduced electrons and holes, and this enhanced the catalytic performance. The degradation efficiency after illumination for 360 min of thin films prepared at oxygen flow rates of 100, 150 and 200 sccm were 87 %, 90% and 92%, respectively.