Three kinds of mechanical relaxations, the alpha, beta, and lambda transitions, of ultradrawn polyethylene films were obtained by dynamic mechanical measurements, and the results were analyzed by positron annihilation. The gels were prepared by crystallization from dilute solutions and were then dried. The dried gel films were stretched by up to a draw ratio of 300 times (lambda = 300). The temperature dependence of the intensity (I-3) of the long-lived component of the orthopositronium (o-Ps) as well as that of the lifetime (lambda(3)) was observed for undrawn and drawn polyethylene films. For the undrawn film, the peak positions of the gamma and transitions corresponded to the first and second transitions Of tau(3). The dispersion was not observed for the films with lambda = 50 and 300. The second transition of tau(3), corresponding to the beta dispersion, was observed for drawn films with A = 50 but was not observed for the film with A = 300. A histogram Of tau(3) for three kinds of specimens showed that the size distribution for the undrawn film (lambda = 1) became broader, and the peak position shifted to a larger value of the lifetime (tau(3)) with increasing temperature. This indicates that the free volume holes within the specimen became bigger and had a wider size distribution with increasing temperature and, at the same time, the molecular motion became more active. For the ultradrawn film with A = 300, the lifetime distribution at 100 degreesC showed a much wider and asymmetry profile, and the peak position shifted to a shorter value than those for the other two films with drawing ratios of lambda = 1 and lambda = 50. This indicated poor activity of a large movement (macro-Brownian motion) of amorphous chains. These experimental results justify that the thermal expansion of the film due to an increase in the molecular mobility was almost zero in a given temperature range from 0 to 120 degreesC and that the storage modulus at 100 degreesC was higher than 130 GPa.