An anti-reflux syringe assembly having a reservoir for containing a fluid, the reservoir having a cylindrical side wall, an open distal end, and a proximal end having a proximal end wall provided at its axial center with a through opening； a piston slidable in leaktight manner in the reservoir, the piston having a distal end adapted to connect to a plunger passing through the open distal end of the reservoir, and a proximal end having a proximal end wall. The proximal end walls of the reservoir and of the piston are conical, and the proximal end wall of the reservoir forms an angle α and the proximal end wall of the piston forming an angle β, with 3°<；α−β<；5°.
