Composites based on the poly(propylene carbonate)-lithium perchlorate system were prepared. Interaction in the poly(propylene carbonate)-lithium perchlorate system in a wide composition interval was studied by IR spectroscopy, differential thermal analysis, and X-ray diffraction. The specific electrical conductivity of the obtained composites was measured. In the series of studied aliphatic polycarbonates, the specific conductivity of the composites increases with an increase in the degree of branching of the polymer.