NOVELTY - A film forming composition comprises titanium oxide, silicon oxide, and organic silicon-type surfactant. The surface tension of the film forming composition with respect to air is 20-35 mN/m, measured by dropping method. The film forming composition has electrophoresis mobility of -5x 10-4 cm2/V.second to -4x 10-4 cm2/V.second at 25 degrees C. The arithmetic mean of average diffusion constant of the film forming composition calculated by analyzing auto correlation function at 25 degrees C is 6.5x 10-8-8x 10-8 cm2/second.    USE - Film forming composition is used for forming reflection preventing film-containing substrate and reflection preventing film-containing solar cell module (all claimed). Uses include but are not limited to photoelectric conversion element, cathode ray tube, liquid crystal display, plasma display panel, anti-reflective film for touch panel, camera lens and optical lithography.    ADVANTAGE - The film forming composition has excellent reflection preventing function. The reflection preventing film formed using film forming composition has high strength and light transmittance for long period of time, and reduced surface contamination. The photovoltaic cell using film forming composition has high electric power generation efficiency.    DETAILED DESCRIPTION - A film forming composition comprises titanium oxide, silicon oxide, and organic silicon-type surfactant. The molar ratio of concentration of silicon with respect to concentration of titanium in the film forming composition is 5-20. The surface tension of the film forming composition with respect to air is 20-35 mN/m, measured by dropping method. The film forming composition has electrophoresis mobility of -5x 10-4 cm2/V.second to -4x 10-4 cm2/V.second at 25 degrees C, measured by electrophoresis laser Doppler method using dynamic-scattering apparatus. The arithmetic mean of average diffusion constant of the film forming composition calculated by analyzing auto correlation function at 25 degrees C is 6.5x 10-8-8x 10-8 cm2/second measured at scattering angle of 90 degrees by cumulant method using dynamic-scattering apparatus. INDEPENDENT CLAIMS are included for the following:    (1) reflection preventing film-containing substrate, which is formed by coating the film forming composition on a substrate and heating;    (2) reflection preventing film-containing solar cell module, which is formed by coating the film forming composition on a solar cell module and heating; and    (3) manufacture of reflection preventing film-containing substrate.