$TiO_2$ and $xTiO_2-ySiO_2$ system photocatalysts were developed by sol-gel method based on the change of production parameters, and their structure of crystallization and the specific surface area was measured. Considering the efficiency of the ethanol decomposition using the catalyst, the conclusion was made as follows: 1) By means of X-ray analysis of $TiO_2$ powder that is obtained from water and Titanium alkoxide with various molar ratios, it is shown that structure of crystallization is a dominating structure and, on the other hand, the crystallization of rutile also partly exists. The specific surface area is at its maximum value at R=6, which is the molar ratio of water vs. alkoxide, whereas its value goes down as the molar ratio increases. In the reaction of using $TiO_2$ catalyst, the ethanol is decomposed into the extent of 15 ~30% in an hour and three hours are necessitated for 70% decomposition. 2) $TiO_2/SiO_2$ powder is developed from Titanium and Silicon alkoxide by a hetero-condensation process. The increase of SiO$_2$ contents causes the decrease of the degree of crystallization of the gel, whereas the specific surface area preferentially increases. In the decomposition reaction of the ethanol, the decomposition efficiency represents 25~60% in an hour. It is, however, examined that the efficiency inactively increases corresponding to the duration of reaction time. It is shown that more than 90% of ethanol is decomposed when reaction time is about three hours and the efficiency illustrates the maximum value for 60-$TiO_2/4O-SiO_2$ catalyst.