The polyethylene oxide (PEO)-based polymer electrolytes containing lithium salts pave the way for the development of safe lithium batteries with high energy storage capacity. Enabled by the flexibly vibrating polymer matrix, the Li-ion transport occurs via hopping along and between the polymer chains. Here, terahertz (THz) time-domain spectroscopy over a frequency range extending from 0.1 THz to 7 THz is applied to investigate the conduction properties of PEO-based electrolytes with lithium salts, and to elucidate the associated dependence of the THz conductivity on the content of the added lithium salt and the electrolyte temperature.