Imidazolium-based ionic liquids (ILs) are widely studied in the biochemical process. In this work, because of the high viscosity of the IL, namely, 1-butyl-3-methylimidazolium acetate, the organic solvents of dimethyl sulfoxide, N,N-dimethylacetamide, and N,N-dimethylformamide were selected as the additives or diluents to reduce the viscosity of IL. The experimental measurements of the viscosity and density were performed at atmospheric pressure in the temperature ranging from (303.15 to 348.15) K. The influences of the organic solvents on the properties of IL were quantitatively analyzed. The excess properties were calculated to further understand the interaction between the IL and organic solvents.