In this work, densities of dimethyl sulfoxide + 1-allyl-3-methylimidazolium chloride mixtures have been experimentally determined with a vibrating tube densimeter. Densities were measured at temperatures between 293.15 and 373.15 K and molar fractions of dimethyl sulfoxide X-DMSO = 0, 0.05, 0.1, 0.15, 0.25, 0.5, 0.75, 0.9 and 1 at pressures in the range P = [0.1, 35] MPa. It was found that density increases with ionic liquid concentration and with pressure and decrease with temperature. Excess molar volumes were calculated resulting in negative values with a maximum of non-ideality at DMSO concentration of X-DMSO = 0.5. The excess molar values were less negative at high pressures. At T = 330 K a maximum in the excess molar values was observed at several concentrations. Density was correlated as a function of temperature, pressure and concentration with an average relative deviation of 0.12%.