The molecular mobility of peroxy radicals at the ends of isolated polystyrene chains (IPSOO) tethered on the solid surface of poly(tetrafluoroethylene) (PTFE) was investigated in a vacuum in the temperature range from 10 to 250 K by electron spin resonance spectroscopy. The onset of an anisotropic tumbling motion of IPSOO at a train state on the PTFE surface was 80 K. When the temperature was above 150 K, the IPSOO protruded from the PTFE surface and resulted in a tail state, in which the IPSOO was in a free rotational state. A train-tail transition temperature was defined at 160 K, which was extremely low compared to the glass transition temperature (373 K) of polystyrene (PS) in the bulk. The activation energy of the IPSOO of the tail state was calculated as 8.3-9.2 kJ/mol. The remarkably high mobility and low activation energy of the IPSOO are probably due to an isolated chain on the PTFE surface, a low chain segmental density, a chain end, and a weak interaction with the PTFE surface.