The paper summarizes conductivity and structural studies of PEO-NH4SCN electrolytes of salt concentration identified by the ether oxygen/ammonium cation ratio ranging between 200 and 3. The impedance and DSC studies are performed during initial heating, cooling and reheating cycles for all salt concentrations. Contrary to previous results recrystallization was observed during cooling, which directly followed the initial heating cycle. Therefore an increase in conductivity observed during cooling can be attributed only to a difference between melting and recrystallization temperatures, the latter of which appears at the lower temperature range. FTIR studies indicate that complexation of ammonium cation via hydrogen bonding to ether oxygen is the most probable way of formation of polymer-salt complex phase. The spectroscopic data suggest that cations are strongly bonded to polyether chains whereas anions are free to move. Therefore charge transfer seems to be due to the transport of anionic species.