Polyiodides (I x − , x=3 and 5) and 2I − …I 2 adducts were established from the Raman spectra study of 1-methyl-3-propylimidazolium iodide (MPIm + I x − ; 1≤x≤5) ionic liquids containing various amounts of iodine (0mol≤I 2 ≤2mol). The existence of I 3 − and 2I − …I 2 was established for 1≤x≤2.5, symmetric I 3 − ions for x=3, while linear and discrete I 5 − was substantiated for 3≤x≤5. The presence of polyiodide species in MPIm + I x − (1≤x≤5) was correlated with an enhanced ionic conductivity, attributed to the established relay-type Grotthus mechanism. Two-step conductivity increase was also reflected in decrease of the hydrogen bond interactions between the CH ring groups and polyiodides. While in the concentration range 1≤x≤3 (triiodides and tetraiodides) IR bands changed only slightly in intensity, in the concentration range x>3 the CH stretching bands (3040–3170cm −1 ) split and the new band at 1585cm −1 appeared in the IR spectra beside the already existing Im + ring stretching mode at 1566cm −1 .