The relationship between the structure and ionic conductivities of the polymer electrolytes formed with the aliphatic polyesters containing a different number of ethylene oxide (EO) units and lithium perchlorate has been investigated. These complexes were observed to be completely amorphous and showed the ionic conductivities up to 10(-5) similar to 10(-4)S/cm at 25 degrees C. The main factor that affects the ionic conductivity in these systems was proved to be a solvating capacity of the matrix polymer caused by the difference in the density of polar groups.