Preparation and characterization of cyclic polystyrenes (c-PS), direct structural observation of one of the derivatives and interdiffusion of c-PS were studied. Cyclic structure of a poly(styrenesulfonate), which was obtained by sulfonation of a c-PS, was directly proved by atomic force microscopic observation. Purities of c-PS were evaluated by high performance liquid chromatography and their values were determined to be higher than 95%. Time evolution of interfacial thicknesses between a cyclic polystyrene (c-hPS) / its deuterated counterpart (c-dPS) and a linear polystyrene (l-hPS) / its deuterated counterpart (l-dPS) bilayer films was investigated by dynamic secondary ion mass spectrometry (DSIMS) and neutron reflectometry (NR). Diffusion coefficient of c-PS is significantly larger than that of the corresponding linear one. This can be explained in terms of weaker topological constraint coming from the less entanglement nature for the c-PS than for the l-PS.