SnO2 thin films were prepared on SiO2/Si substrate by RF-Magentron Sputtering method, varying the deposition time and Ar-to-O-2 flow ratio. The post-annealing was conducted at 500 degreesC and 700 degreesC in Ar and O-2 atmosphere, respectively. Film characteristics were very sensitive to the gas flow ratio during the deposition and the conditions of post-annealing. The Film thickness decreased with decreasing of Ar flow ratio at a constant amount (50 seem) of total gas flow. Especially, the film deposited under Ar-O-2 mixture gas (Ar-to-O-2 ratio of 50%) showed clearly aggregated morphology of small particles (cauliflower) in a wide range of area. In the annealed films, these cauliflowers separated some small grains, decreasing the film thickness.