An adjustable expansion card retainer comprises a first supporting frame and a second supporting frame with a front end thereof pivotally coupled to a rear end of the first supporting frame; a compressing end of the first supporting frame can be rotated to a proper angle relatively to a lower side of the second supporting frame. The compressing end of the first supporting frame is allowed to adjust downward amount movement substantially by sliding a first slide unit of the first supporting frame forward a proper distance relatively to a first fixing unit. Whereby, various expansion cards with different height can be respectively compressed to enable an auxiliary expansion card retainer to be suitable for fixing various expansion cards with different height.