An Ag-controlled co-plating method was developed for the preparation of palladium/silver alloy membranes on porous tubular alumina supports. By controlling the feed rate of Ag to the Pd bath, the concentration of the silver in the plating bath was restricted during the course of plating. As a result, preferential deposition of silver at the beginning was suppressed and uniform dispersion of silver inside the membrane with silver composition in the desired range was achieved. Ultrathin (similar to 2.5 mu m) PdAg alloy membranes with uniform silver composition of similar to 25% were successfully obtained. The membrane showed a hydrogen permeance of 0.88 mol m (2) s(-1) and pure-gas H-2/N-2 selectivity of 2140 at 823 K with Delta P = 100 kPa. Only one hydride phase existed in the studied temperature range from 373 to 823 K with Delta PH2 = 100 kPa. Direct comparisons with the conventional simply-mixed co-plating method showed that membranes made by the novel Ag-controlled co-plating method had much more uniform silver distribution, smoother surface, denser membrane structure, higher utilization rate of metal sources, and shorter alloying time. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.