A simple preparation method has been developed for creating inorganic organic composite films by casting of soft poly(butadiene) (PB) particles and hard SiO2 particles. PB particles were successfully prepared by evaporation of a good solvent from the PB solution containing water as a poor solvent. After crosslinking PB and removal of SiO2 particles, an inverse opal structure can be formed. The size difference between PB and SiO2 particles critically determines the coassembling structures.