A fixing system for a spare wheel for a motor vehicle of the type is provided with a housing for said spare wheel, said fixing system comprising a first element with a first threaded end, which can be fixed to a bottom wall of said housing, also comprising a clamping nut and a metal fixing screw which comprises a threaded shaft and is coupled with said clamping nut in order to constrain said spare wheel inside said housing. Said first element comprises a central metal body with a second end provided with a threaded hole, and said first threaded end being screwed into said bottom wall of said housing, in order to block the position of said first element and to permanently fix the same to said housing, said threaded shaft of said fixing metal screw being screwed into said threaded hole of said second end of said central metal body, in order to make said fixing metal screw integral with said first element, furthermore said first element comprising an outer polymeric portion made of a polymeric material which envelops said central metal body.