The mutual diffusion coefficient (D-12) of [mmim]DMP (1-methyl-3-methylimidazolium dimethylphosphate)/H2O and [mmim]DMP/CH3OH at ionic liquid (IL) mass fraction (omega(1)) of 0.005-0.995, atmospheric pressure of 101.5 kPa, and temperature (T) of 298.15-328.15 K were measured using the holographic interferometry. It is the first time to employ holographic interferometry to measure the D-12 of binary solutions containing ionic liquid. The influence of the meniscus on the determination of the initial time for diffusion is discussed for the first time. And this influence is eliminated by using a fitting method. D-12 of [mmim]DMP/H2O and [mmim]DMP/CH3OH increase with the increase of temperature, and decrease with the increase of the IL mass fraction. The experimental data of [mmim]DMP/H2O and [mmim] DMP/CH3OH were correlated using the modified group contribution model, with the total deviations below 4.7% and 4.2%, respectively. The relationship of the mutual diffusion coefficients is [mmim] DMP/CH3OH > [mmim]DMP/H2O > LiBr/H2O on the same conditions. The studies on D-12 establish the foundation for the design and optimization of the absorber of ionic liquid absorption systems. (C) 2017 Elsevier Ltd. All rights reserved.