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The phase diagram of mixed monolayers composed of distearoilphosphatidylcholine (dspc) and dimiristoilphosphatidylcholine (dmpc) contains a one-phase zone for low mole % of dspc and a two-phase zone for higher dspc concentrations. At 10 mN m-1 the coexisting phases are composed of 20 mole% dspc and almost pure dspc, respectively. In this work we study the mechanical properties at 10 mN m-1 of mixed monolayers of dspc:dmpc in different proportions. We find that the isothermal compressibility modulus shows a non-ideal behavior with the mole fraction, as expected considering the phase diagram of the mixture. The compressibility of the monolayer is independent of the dspc amount in the mixture up to about 50% of dspc. For higher dspc content, the modulus increases linearly. This is related to an increase of the dissipative component of the modulus which also increase linearly with the mole fraction of dspc for x>0.5. On the contrary, the elastic storage component remains the same, within error, for different monolayer proportions. In the two-phase zone, the compressibility should be related with the amount and distribution of each phase. In this sense, the dependence of the mechanical properties with the percent of monolayer area in the condensed state (%An) was studied. For %An bellow about 35%, the isothermal compressibility modulus and the dissipative component are independent of %An, while for higher percents, both parameters increase linearly. In conclusion, the presence of the condensed domains influences the compressibility only if the percent of condensed area is above a critical value. We also determined the diffusion coefficient of the domains for different %An and found that, compared to the compressibility the shear viscosity is influenced by the presence of the condensed state at lower %An.