The pulsing system of the slow positron beam has been developed in order to measure positron lifetime in polymer thin films. The time resolution of the system has been similar to370 ps (FWHM). Doppler broadening and positron lifetime measurements are performed as a function of positron incident energy for polystyrene-polystyrene bilayers. Positron behavior and interface structure in the bilayers are discussed in the present study. (C) 2002 Published by Elsevier Science B.V.