A mixer valve of hot and cold water is described, for sanitary fixtures, provided with a pressure balancer of the inlet flows of cold water and hot water. If need be, the valve can also be provided with a temperature regulator and/or a multi-way diverter. The pressure balancer comprises a cylindrical element in which two inlet chambers of cold water and hot water are defined and separated by a movable plunger. When a pressure variation occurs in one of the two inlet flows, the plunger moves correspondingly thus modifying the volume of one of the two chambers, in order to compensate the pressure variation not transmitted to the flows sent to the downstream mixer cartridge. The pressure balancer is coaxial to the other valve components. Advantageously, the movable plunger slides along the longitudinal axis of the valve.