Blending methyl ester biodiesel and ethyl ester biodiesel can improve the properties of biodiesel. The densities and viscosities of the mixtures of methyl dodecanoate plus ethyl octanoate with various compositions were reported at temperatures from 303.15 to 323.15 K and at pressures up to 15 MPa. Experimental data show that the densities and viscosities of the mixtures of methyl dO-decanoate plus ethyl octanoate will increase when temperature decreases or pressure increases. Ethyl octanoate can effectively reduce the viscosity of methyl dodecanoate with a small change in density. Correlations for the data of density and viscosity were proposed with maximum absolute relative deviations less than 0.04 and 5.8%, respectively.