Abstract The dielectric constant of 1-MeIm–water mixtures with entire mixture range has been determined in the frequency range 20MHz to 20GHz at 298K using the dielectric relaxation spectroscopy (DRS) method. Mixture dielectric behavior is well described by the Cole–Cole model. We estimated H-bonds effect for molecular interactions by the excess dielectric model. The type of dipolar orders by which depends on the extent of substitution and cooperative interaction of 1-MeIm–water cluster are also calculated by Luzar model and extended Froehlich theory. We get different aspect of the interaction of molecules, which can help us have a deeper understanding of relaxation acts.