Poly(n-butylamino) (di-allylamino)phosphazenes were prepared by the reaction of (NPCl2)(n) with n-butylamine and di-allylamine. After the membranes were prepared by the casting method, they were irradiated by ultraviolet electron beam, Co-60 gamma-rays. It was found from Fourier transform-infrared data that the CH=CH2/N-H ratios of the irradiated membranes decreased with increasing dose. Also, the membrane did not dissolve in tetrahydrofuran or other organic solvents. This supported the idea that the CH=CH, bond was cleaved by the irradiation and the cross-linking occurred intermolecularly. Oxygen gas permeability values, D-k, of the irradiated membrane were determined from oxygen permeability and mechanical properties were determined with a Tensilon instrument. D-k values decreased with increasing Young’s modulus in the case of low concentrations of di-allylamine.