NOVELTY - The process for purification of hydrogen contained in a synthesis gas after passing it in a high temperature water gas shift unit, comprises introducing a mixture (1) to be treated in a first membrane separation unit to extract a first permeate (3) constituted of hydrogen and a first retentate (4), introducing the first retentate in a second membrane separation unit to extract a second permeate (5) and a second retentate (7), and passing the first permeate to a third membrane separation unit after repressuring to extract a third permeate and a third retentate.    USE - The process is useful for the purification of hydrogen contained in a synthesis gas after passing it in a high temperature water gas shift unit, where the purified hydrogen is useful in a fuel cell for generating electricity and in agri-food industry for the treatment of oils (all claimed).    ADVANTAGE - The process ensures effective, economical and rapid purification of hydrogen contained in a synthesis gas thus providing 98% of pure hydrogen and carbon monoxide (10 ppm) with a recovery rate of higher than 85 mass%.    DETAILED DESCRIPTION - The process for purification of hydrogen contained in a synthesis gas after passing it in a high temperature water gas shift unit, comprises introducing a mixture (1) to be treated in a first membrane separation unit to extract a first permeate (3) constituted of hydrogen and a first retentate (4), introducing the first retentate in a second membrane separation unit to extract a second permeate (5) and a second retentate (7), passing the first permeate to a third membrane separation unit after repressuring to extract a third permeate and a third retentate, and recycling the second permeate and the third retentate to an entrance of the first membrane separation unit. Each separation unit has a pressure difference of 10-30 bars between their upstream and downstream, and an operating temperature of 20-250?0C. The membrane of each separation unit has a permeability of higher than 50 barrer, and hydrogen selectivity of higher than 30 with respect to carbon monoxide. When the synthesis gas is produced by vapor reforming, the second retentate is used as a fuel in the vapor reforming furnace.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a process for the purification of hydrogen.    Mixture to be treated (1)    First permeate (3)    First retentate (4)    Second permeate (5)    Second retentate. (7)