In this work, palladium-silver alloy membranes were prepared by electroless codeposition technique. The effects of plating time and heat treatment on the surface morphology and composition of the deposited PdAg layer were investigated by means of SEM, XRD and EDS. The pore structure of the resultant composite membranes was also characterized by the nitrogen permeability technique. The experimental results show that the mole fraction of Ag in the,deposited layer is increased from 0.23 to 0.38 as the plating time increases from 4 to 8 h. Moreover, as the plating time increases, the PdAg co-deposited layer tends to be more dendritic. These are attributed from different deposition rates of Pd and Ag. After heated at 750degreesC for 12 h in argon atmosphere, instead of densification, the sintering of PdAg grains causes many voids remaining in the PdAg layer. Hence, the nitrogen permeability across the PdAg layer is increased with increasing the plating time. The average pore size of the PdAg layer is determined as about 0.32 mum, and almost independent on the plating time within 8 h. The dendritic structure of PdAg/Al2O3 composite membranes resulting in the vast leakage of nitrogen, however, is difficult to be improved by way of heat treatment.