The positron lifetime spectra and ionic conductivity have been measured for poly(ether urethane)‐LiClO4polymeric electrolyte as a function of temperature. The glass transition temperatureTg, free‐volumeVf, and fractional free‐volumefwere derived from the positron annihilation parameters. A correlation between fractional free‐volumef(T) and conductivity &sgr; aboveTg, log[&sgr;/&sgr;(Tg)]=C1[f(T)−f(Tg)]/f[T], was first experimentally confirmed using measured positron annihilation results. The comparison of the value of the obtained constantC1with the universal values for the segmental diffusion of amorphous polymers indicated that the critical free volume required for the ion transport is much smaller than that required for polymer chain segment mobility. Carrier transport and the segmental motion are discussed in terms of the free‐volume theory. ©1995 American Institute of Physics.