The present invention relates to units for separation of gas mixtures using hollow fiber membranes and may be used in chemical, oil, gas and other industries. More specifically, this invention relates to the structure of the membrane gas separation module which may be applied, for instance, in membrane separation units for helium concentrate. The membrane gas separation module comprises the horizontal body with end covers and membrane cartridges made of a bundle of hollow fibers and located in an inversed manner in relation to the center. The body comprises symmetrical end sections of large diameter which are mated by conical transition sections with the central section of minor diameter. In this case length of end sections corresponds with length restricted by the body end and input area of membrane cartridges, and central section inner diameter is configured to provide both free mounting/dismounting of membrane cartridges and tight fit thereof at the sealing point with ring gaskets. Feed gas input nozzles are located on end sections of the body perpendicularly to its longitudinal axis in front of input areas of membrane cartridges, permeate output nozzles are located on end sections of the body near end covers perpendicularly to the body longitudinal axis. The technical result is reduction of weight and dimensional properties of the membrane module and the whole gas separation unit in general, as well as reduction of labor intensity of operations during mounting/dismounting of body end covers of the membrane module.