A demountable wall partition system comprising a first and a second demountable partition panel (10, 10'), and a flange connection element, wherein each of the a first and a second demountable partition panel (10,10') has a front surface (12,12'), a rear surface (13,13') and side edges connecting the front surface (12,12') and the rear surface (13,13'), and comprises a board (11,11') having a rear surface (13,13') forming the rear surface (13,13') of the associated demountable partition panel (10,10') and at least one panel mount bracket (20,20') connected to the board (11,11') and protruding from the rear surface (13,13'), the at least one panel mount bracket (20, 20') comprising a first end flange extending in a first flange plane parallel with the rear surface (13,13') of the board (11,11'), and a second end flange, wherein the first and second demountable partition panels (10, 10') are arranged spaced apart with the rear sides (13, 13') facing each other such that the at least one panel mount bracket (20, 20') of the respective first and second demountable partition panel (10, 10') form at least one pair of aligned panel mount brackets (20, 20'), wherein the board of at least one of the first and second demountable partition panel (10,10') is a gypsum board and more preferably a reinforced gypsum board, characterized in that the at least one pair of aligned panel mount brackets (20, 20') are connected to each other by means of the flange connection element which is connected to the second end flanges of the at least one pair of aligned panel mount brackets (20, 20') such that the flange connection element is supported by the at least one pair of aligned panel mount brackets (20, 20'). a first and a second demountable partition panel (10, 10'), and a flange connection element, wherein each of the a first and a second demountable partition panel (10,10') has a front surface (12,12'), a rear surface (13,13') and side edges connecting the front surface (12,12') and the rear surface (13,13'), and comprises a board (11,11') having a rear surface (13,13') forming the rear surface (13,13') of the associated demountable partition panel (10,10') and at least one panel mount bracket (20,20') connected to the board (11,11') and protruding from the rear surface (13,13'), the at least one panel mount bracket (20, 20') comprising a first end flange extending in a first flange plane parallel with the rear surface (13,13') of the board (11,11'), and a second end flange, wherein the first and second demountable partition panels (10, 10') are arranged spaced apart with the rear sides (13, 13') facing each other such that the at least one panel mount bracket (20, 20') of the respective first and second demountable partition panel (10, 10') form at least one pair of aligned panel mount brackets (20, 20'), wherein the board of at least one of the first and second demountable partition panel (10,10') is a gypsum board and more preferably a reinforced gypsum board, characterized in that the at least one pair of aligned panel mount brackets (20, 20') are connected to each other by means of the flange connection element which is connected to the second end flanges of the at least one pair of aligned panel mount brackets (20, 20') such that the flange connection element is supported by the at least one pair of aligned panel mount brackets (20, 20').