Thermostatic gas valve with a pressure regulator The thermostatic gas valve (1) is adapted for delivering gas flows (7′,8′) to a main burner and to a pilot burner of a heater appliance and comprises a valve body (3) with a plurality of internal gas distribution chambers (4,5,5′) interconnected to a manual valve (11), to a main flow (7′) thermostatic modulating device (12), and to an electromagnetic safety valve (9) energised by a thermocouple (10), between a gas inlet duct (6) and outlet ducts (7,8) for said flows (7′,8′). An inlet pressure (Pe) regulator device (2) provided with a diaphragm type stabilising valve (18,19), is inserted in said inlet duct (6) in direct communication with the safety valve (9) via a flat conduit (27) under a valve body cover (14).