Molecular aggregation structure of poly(fluoroalkyl acrylate) [PFA-Cy, where y is the fluoromethylene number of the fluoroalkyl (R-f) groups] thin films was characterized by grazing-incidence X-ray diffraction (GIXD). In-plane diffractions corresponding to the hexagonal packing of the R-f groups were measured for PFA-C-y with y >= 8 in the surface and bulk regions. This result indicated that the R-f groups were oriented almost perpendicular to the film surface.