Dissociation equilibria of lithiumthiocyanate (LiSCN) in N,N-dimethylformamide (DMF) solutions of poly(propylene oxide) (PPO) were investigated by using infrared spectroscopy. The stretching bands due to the thiocyanate ions SCN-1 and the LiSCN ion pair were found at 2058 and 2072 cm(-1), respectively. At high LiSCN concentration C of ca. 20 wt %, another weak band due to the dimer (LiSCN)(2) was observed. From the ratio of the areas of the absorption bands, the dissociation constant K-1 for the equilibrium LiSCN reversible arrow Li+ + SCN-1 and that K-2 for (LiSCN)(2) reversible arrow 2LiSCN have been determined. With increasing DMF content, K-1 increases from 1 X 10(-4) for bulk PPO to 4.8 X 10(-1) for pure DMF at 299 K. Log K-1 is not linear against inverse of the dielectric constant epsilon of the medium and decreases with increasing temperature. The enthalpy (Delta H) and entropy (Delta S) changes for the dissociation of LiSCN are both negative.