A patterning process which uses self-assembly, wherein the patterning process includes: forming a silicon-containing film by applying a silicon-containing film composition having an organic substituent group substituted with an acid labile group onto a substrate to be processed, pattern-exposing of the silicon-containing film, forming a polymer film by applying a self-assembling polymer onto the silicon-containing film, self-assembling the polymer film to form a microdomain structure, forming a pattern on the polymer film, transferring the pattern to the silicon-containing film by using the pattern formed on the polymer as a mask, and transferring the pattern to the substrate to be processed by using the pattern transferred to the silicon-containing film as a mask. There can be provided a pattern having a microdomain structure formed by self-assembly with excellent uniformity and regularity, the pattern having been difficult to be obtained by a conventional self-assembly polymer.