Device for retracting a piston for a brake caliper, said brake caliper comprising a caliper body arranged astride of a brake disc having friction surfaces (6, 7) perpendicular to a rotation axis (X-X) defining an axial direction, and opposite pads received in said caliper body so as to be able to slide in the axial direction to the brake disc to act respectively on said opposite friction surfaces (6, 7), said caliper body also comprising at least one piston seat suitable for receiving the piston equipped with a side surface suitable for sliding in said piston seat so as to be able to be biased by a brake fluid coming out from said seat to influence at least one of said pads against said friction surfaces (6, 7) of the brake disc, wherein said device comprises: - an annular seat coaxial with said piston seat, said annular seat having an axial abutment surface perpendicular to said axial direction and arranged in the direction of output of the piston, and a radial bottom surface arranged facing said side surface of the piston; - at least one elastic element arranged in said annular seat, with a first radial surface thereof in contact with force against said side surface of the piston and with a second radial surface thereof in contact with force against said radial bottom surface of the annular seat; - at least one elastic ring housed in said annular seat and axially (interposed) arranged between said at least one elastic element and said axial abutment surface, on the opposite side to the brake fluid, said ring having an inner perimeter surface and an outer perimeter surface, between said inner perimeter surface and said side surface of the piston forming a first annular chamber open towards the side surface of the piston and towards the elastic element; - a second chamber facing said outer perimeter surface and arranged between said outer perimeter surface and a portion of said radial bottom surface of the seat, characterized in that - said ring being radially elastically deformable varying between a rest configuration and a dilated configuration, and wherein - said second chamber is suitable for allowing the deformation of the ring up to its dilated configuration, - said second chamber is substantially continuous and annular, wherein said ring comprises lightening means suitable for facilitating the radial deformation of the ring when biased and said lightening means are alternatively selected from the group consisting of: - said lightening means comprise a plurality of recesses or holes passing through axially, each said through recess or hole being arranged in a respective tooth or - said lightening means comprise at least one circumferential channel made along said ring or - said lightening means comprise at least one axially open inner radial recess or - said ring comprises a plurality of inner recesses and a plurality of outer recesses or - said ring has a radial thickness of between 0.6 and 0.8 mm. - an annular seat coaxial with said piston seat, said annular seat having an axial abutment surface perpendicular to said axial direction and arranged in the direction of output of the piston, and a radial bottom surface arranged facing said side surface of the piston; - at least one elastic element arranged in said annular seat, with a first radial surface thereof in contact with force against said side surface of the piston and with a second radial surface thereof in contact with force against said radial bottom surface of the annular seat; - at least one elastic ring housed in said annular seat and axially (interposed) arranged between said at least one elastic element and said axial abutment surface, on the opposite side to the brake fluid, said ring having an inner perimeter surface and an outer perimeter surface, between said inner perimeter surface and said side surface of the piston forming a first annular chamber open towards the side surface of the piston and towards the elastic element; - a second chamber facing said outer perimeter surface and arranged between said outer perimeter surface and a portion of said radial bottom surface of the seat, characterized in that - said ring being radially elastically deformable varying between a rest configuration and a dilated configuration, and wherein - said second chamber is suitable for allowing the deformation of the ring up to its dilated configuration, - said second chamber is substantially continuous and annular, - said lightening means comprise a plurality of recesses or holes passing through axially, each said through recess or hole being arranged in a respective tooth or - said lightening means comprise at least one circumferential channel made along said ring or - said lightening means comprise at least one axially open inner radial recess or - said ring comprises a plurality of inner recesses and a plurality of outer recesses or - said ring has a radial thickness of between 0.6 and 0.8 mm.