The local motion of polystyrenes in dilute solutions was examined by the fluorescence depolarization technique. The samples, polystyrene (PS), poly(alpha-methylstyrene) (P alpha MS), and poly(p-methylstyrene) (PpMS), were labeled with the fluorescent probe anthracene in the middle of the main chain. The relaxation time of their local motion in dilute solutions was examined by fluorescence anisotropy measurement. The activation energy of the relaxation time of the polymer chain, E*, was also evaluated by the theory of Kramers’ diffusion limit. There was a close correlation between the reduced relaxation time, T-m/eta, or its activation energy and the chain expansion factor; i.e., both the reduced relaxation time and the activation energy decrease as the solvent quality becomes better. The reduced relaxation time and the activation energy depended on the local segment density of the polymer chain in the solution. The local motion for each polymer was compared in a theta solvent. The relaxation time and the activation energy of P alpha MS were larger than those of PS. This indicated that the barrier height of the local motion for a disubstituted polymer chain is higher than that for a monosubstituted one. Furthermore, the relaxation time and the activation energy of the PpMS chain were larger than those of PS.