The method of liquid phase deposition (LPD) has an interesting feature that some kinds of organic compounds can be directly doped into silica layers. We doped a cyanine dye (1-ethyl-2-[3-chloro-5-(1-ethyl-2(1H)-quinolylidene)-1,3-pentadienyl] quinolinium bromide) in silica thin films by using the LPD method and observed thermochromic behavior of the prepared samples. The samples are colorless just after preparation. When they are maintained at a raised temperature, they turn blue. The origin of this thermochromic behavior has been attributed to the elimination of water molecules out of silica phases. A semi-empirical MO calculations also support the proposed mechanism.