Surface glass transition behaviors of monodisperse alpha,omega -diamino-terminated and alpha,omega -dicarboxy-terminated polystyrenes (alpha,omega -PS(NH2)(2) and alpha,omega -PS(COOH)(2)) were studied by scanning force microscopy and were compared with the results of proton-terminated polystyrene (PS-H). All surface glass transition temperatures, T-g(s), of PS-H, alpha,omega -PS(NH2)(2), and alpha,omega -PS(COOH)(2) were discernibly lower than each corresponding bulk glass transition temperature, T-g(b). However, the magnitude of T-g(s) was strongly dependent on the chemical structure of chain end groups, because the surface concentration of chain ends varied with the surface free energy difference between the main chain part and the chain end portion, via the surface segregation or surface depletion of chain ends. This result makes it clear that chain end chemistry is one of determining factors on the magnitude of T-g(s). On the basis of the time-temperature superposition principle applied to the scanning rate dependence of lateral force as a function of temperature, the apparent activation energy, DeltaH(double dagger), of the alpha (a)-relaxation process corresponding to micro-Brownian motion at the surface was evaluated to be approximately 230 kJ mol(-1). This value is much smaller than the reported bulk ones and is independent of the chemical structure of chain ends. This result implies that the cooperativity for the alpha (a)-relaxation process at the PS surface is reduced in comparison with the bulk, probably due to the existence of the free space presented to polymer segments at the surface. Hence, it was concluded that the surface alpha (a)-relaxation process was activated by not only the chain end effect but also the reduced cooperativity at the surface. Finally, possible other factors determining on the magnitude of T-g(s) were discussed.