Abstract: Support system for auxiliary power unit which sustains an auxiliary power unit (1) of an aircraft to a fixed structure (2) belonging to a compartment of the auxiliary power unit (6) of said aircraft, made in a high mechanical strength material, and with high resistance to ignition, which comprises at least three fittings (3, 4, 5) of a substantially cylindrical shape, said fittings (3, 4, 5) being able to be hollow, and each one of them presenting a first end (7) comprising means of attachment of the support system (8) to the fixed structure (2) and a second end (9) comprising means of securing of the support system (8) which are joined to the auxiliary power unit (1) in the periphery of the extension of said auxiliary power unit (1), with at least a first forward fitting (4) and a second forward fitting (5) being located in the forward part of the auxiliary power unit (1), and at least one rear fitting (3) being located in the rear part of the auxiliary power unit (1).