A dispenser includes a hollow containment body (2) able to be inserted in a bottle and including an orifice (5) for the suction of liquid from the bottle, a ring nut (21), able to be screwed onto the neck of the bottle, including an annular shoulder (22) covering and associated to an annular lip (2d) of the containment body. The dispenser further includes a piston (10) able to slide within the containment body between a raised position and a lowered position, a hollow stem (7) axially able to slide within the containment body, associated inferiorly to the piston and superiorly to a dispensing spout (8) to command the actuation of the piston and dispense fluid contained in the bottle. Also provided is a retaining ring (11) integral with the containment body and inserted therein to guide the stem in its travel within the containment body.