The performances of filled and unfilled poly[1-(trimethylsilyl)-1-propyne] (PTMSP) membranes have been investigated.1) to describe through a mathematical model the performance decay which takes place during the pervaporation of organics from aqueous streams with PTMSP membranes;2) to test and understand how the presence of adsorptive and non-adsorptive fillers acts to modify the performances of these membranes. So some criteria can be drawn to choose the right filler and its best concentration.The interpretation of the experimental results with the filled membranes is accomplished by a model for the diffusion in a composite system that is constituted by the continuous polymeric phase with the dispersed filler particles.It is concluded that the fillers hinder the decay of the flux and of the selectivity. Furthermore, in order to improve the performances, the filler must possess a high sorption selectivity accompanied by a favorable value for the ratio of the diffusivity of organics to that of the water.