The invention discloses a rear brake caliper piston, and aims to provide a rear brake caliper piston which is good in structural strength, capable of dissipating heat easily and resistant to abrasion.According to the technical scheme, the rear brake caliper piston mainly comprises a piston body; the piston body comprises a first main body and a second main body which are connected with each other; the axis of the second main body is provided with a step hole which is of a multi-section structure and penetrates through the second main body; the end, right facing the second main body, of the first main body is provided with an inner hole communicating with the step hole; the end, away from the second main body, of the first main body is provided with a heat dissipation groove, and the groove bottom of the heat dissipation groove is provided with two positioning holes which are symmetrical about the axis; the peripheral wall of the first main body is provided with a clamping groove whichis of an annular structure, and an air exhaust groove which is of an annular structure, and the air exhaust groove is provided with an air exhaust hole communicating with the inner hole; the second main body is provided with a plurality of micropore structures, and a plurality of micropores form oil way channels communicating with the inner wall and the outer wall of the second main body; and theend, away from the inner hole, of the step hole is provided with a liquid storage groove. The rear brake caliper piston is suitable for the technical field of pistons.