The invention provides a patterning process for forming a negative pattern by lithography, comprising at least the steps of: using a composition for forming silicon-containing film, containing specific silicon-containing compound (A) and an organic solvent (B), to form a silicon-containing film; using a silicon-free resist composition to form a photoresist film on the silicon-containing film; heat-treating the photoresist film, and subsequently exposing the photoresist film to a high energy beam; and using a developer comprising an organic solvent to dissolve an unexposed area of the photoresist film, thereby obtaining a negative pattern. There can be a patterning process, which is optimum as a patterning process of a negative resist to be formed by adopting organic solvent-based development, and a composition for forming silicon-containing film to be used in the process.