FT-IR spectra of P(EO)(n)MSCN polymer electrolytes have been recorded at room temperature from n = 6-80. The peaks located at - 2037 and - 2043 cm(-1) were respectively assigned to SCN- stretching mode in crystalline complex and contact ion-pair dimer of NaSCN. It was shown that the free SCN- and the crystalline complex were formed in PEO-NaSCN, but they were not observed in PEO-KSCN system. The PEO-KSCN electrolytes exhibit the amorphous characteristics, which make the contact ion pairs, and the solvent-separated dimers are main ion species in this system. The contact ion-pair dimers can be formed in both systems as the ability of PEO chain to wrap cation is reduced with increase salt content. These conclusions are used to explain the experimental results of conductivity for PEO-MSCN polymer electrolytes. (C) 2003 Elsevier B.V. All rights reserved.