Two guanidinium-based ionic liquids (ILs), 2-ethyl-1,1,3,3-tetramethylguanidinium bis(trifluoromethylsulfonyl)imide ([TMGEt] [NTf2]) and ethyl sulfate ([TMGEt][C2OSO3]) were synthesized and characterized. Experimental densities and viscosities for the binary mixtures of the ILs with ethanol and 1-propanol from (293.15 to 323.15) K were measured over the whole composition range and at the atmospheric pressure of 0.1 MPa. The excess molar volumes (V-m(E)) and the viscosity deviations (Delta eta) for the binary systems were calculated and fitted with the Redlich-Kister equation. It is found that the density of [TMGEt] [NTf2] is much higher than that of [TMGEt][C2OSO3] at the same temperature, while the viscosity of the former with the value of 74.61 mPa.s is only 1/9 of that of the latter at 293.15 K. This indicates that the difference of the anions has a significant influence on the density and viscosity of the ILs with the same guanidinium cation. The addition of ethanol or 1-propanol leads to negative values of V-m(E) and Delta eta which result from the efficient packing of the constituents in the binary mixtures and the weakening of anion-cation interactions of the ILs. The partial molar volumes, excess partial molar volumes, Gibbs energy, and excess Gibbs energy of activation for viscous flow of the binary mixtures also have been calculated. It is hoped that the results provide useful information for the fundamental physicochemical properties of the guanidinium-based ILs and their further applications.