In this study we have used molecular dynamics simulations to understand at the molecular level the causes for the quasi-ideal behavior of mixtures of two ionic liquids having two cations of the same homologous series and a common anion. For this purpose, we have modeled an equimolar mixture of 1-ethyl-3-methylimidazolium and 1-hexyl-3-methylimidazolium bistriflamide, ([C 2 mim][NTf 2 ] +[C 6 mim][NTf 2 ]) at 303 K and p = 0.1 MPa and analyzed its structure using the corresponding pair radial distribution functions obtained from the simulation trajectories. For comparison purposes we have also carried-out simulations under the same conditions of the two pure ionic liquids used in the mixture and also of the ionic liquid 1-butyl-3-methylimidazolium bistriflamide, [C 4 mim][NTf 2 ]. The estimated excess volume of the mixture, showing a very small deviation, agrees with experimental results.