© 2020 Elsevier B.V. The spatial structures of polystyrene (PS) nanocomposite thin films containing oleic acid-modified nanoparticles were investigated. A layer of the nanoparticles was formed at the surface of the thin film under all conditions in this work. Aggregates of the nanoparticles were formed simultaneously in the film when the concentration of the nanoparticles was relatively high. The effects of the evaporation rate and the molecular weight of PS on the spatial structures of the nanoparticles in the thin films were discussed using the ratio of the time constants for phase separation (diffusion) of the nanoparticles, gravitational sedimentation of the aggregates and drying. As the ratio of the diffusion time to the drying time increased, the thickness of the nanoparticle layer and the diameter of the nanoparticle aggregates decreased, and then reached a constant value. When the ratio of the sedimentation time to the drying time was high, the relatively small aggregates were dispersed throughout the thin film since the effect of gravitational sedimentation was small.