Morphology and stress relaxation of oriented polyolefin films has been studied. The influence of orientation on morphology of the films has been investigated using X-ray, DSC, and TEM. The relaxation time spectrum of oriented films has been investigated. It was shown that relaxation time spectrum of composite film can be predicted if one knows the relaxation time spectrum of each component in the film. An influence of irradiation on relaxation behavior of polyethylene film was shown as well. (C) 2003 Wiley Periodicals, Inc.