A new type of siloxane-phosphazene copolymer system has successfully been synthesised via hydrosilylation of a high molecular weight polyaryloxyphosphazene, with oligo-H-polysiloxanes of different molecular weight, allowing the preparation of different materials having an increasing PDMS content up to 80 wt%. The starting hydrogeno siloxanes used were quantitatively grafted and led to cross-linked structures characterized as a microphase-separated copolymer system. Thin films of good mechanical properties up to 60 wt% of PDMS were prepared. The transport properties of the films for the permeants n-butanol, water and their saturated mixture have been determined by sorption, desorption and pervaporation measurements. It was established that all the tested materials have a stronger affinity for butanol than for water and that the difference in transport properties in the series is mainly based on the type of continuous phase. Up to 40 wt% of PDMS, the continuous phase consisted of poly(phosphazene) having a lower diffusion ability, whereas for higher values, the continuous matrix turns to PDMS phase which leads to a considerable permeability increase. For a PDMS content of 60 wt%, the selectivity reached is similar to that of polydimethylsiloxane itself.