A device for dosing fluid products comprises a substantially hollow main body (2), fully insertable into a container for a fluid product; a piston (7) slidably movable in the main body (2) defining, in combination with the main body (2), a dosing chamber (8) presenting a containment volume for the fluid product having a capacity as a function of the relative position between the piston (7) and the main body (2); a stem (10) operatively active on the piston (7) to actuate the piston; the stem (10) being slidably movable between a first operative position in which the volume of the dosing chamber (8) is greatest and a second operative position in which the volume of the dosing chamber (8) is smallest; the stem (10) being hollow and in fluid communication with the dosing chamber (8) to expel a portion of fluid. The main body (2) comprises a tubular portion (3) connected to a closing ring (41) in proximity to the upper end (2a) of the main body (2); the closing ring (41) further comprising a sleeve (18) that encompasses the stem (10) and is in sliding contact therewith.