In the present study, the synthesis, characterization and permeability of polyamide membranes for encapsulation use are reported. The membranes were formed by polycondensation at the interface between an organic solution of terepthaloyl dichloride and a hydrogel substrate, swollen to an amine aqueous solution. Different membranes were prepared by varying either the molar ratio of diethylene triamine to terephthaloyl dichloride or by using mixtures of diethylene triamine with a second amine (e.g. ethylene diamine, 1,6-hexamethylene diamine or triethylene tetramine). The polyterephthalamide membrane morphology, its equilibrium water content and thermal behavior, the partition coefficient and the membrane permeability to NaCl are experimentally investigated. Finally, the effects of the ionic strength and pH of the release medium on the permeation characteristics of the polyterepthalamide membranes are experimentally determined.