In order to achieve a deeper understanding about the nature of interactions in the mixtures of polyethylene glycol (PEG) and ionic liquids (ILs), interactions between polyethylene glycol and 1-alkyl-3-methylimidazolium bromide ionic liquids mixture were studied via proton nuclear magnetic resonance ((HNMR)-H-1) and ultraviolet-visible (UV-Vis) spectroscopy techniques. The variation of peaks position in the (HNMR)-H-1 spectra may be attributed to the hydrogen bonding between H-C-2 hydrogen of imidazolium based ionic liquids and ethoxy group, -O-, of PEG. The obtained results from UV-Vis spectroscopic reveal that decreasing the absorption intensity of imidazolium based ionic liquids in the presence of PEG related to existence hydrogen bound between PEG and imidazolium cation. Density functional theory (DFT) method was also performed to confirm hydrogen bound between PEG and ionic liquids. (C) 2018 Elsevier Ltd.