In a pressure motor for electro-rheological fluids comprising a housing (1) surrounding two operating chambers (A, B), a piston (3) moveable in the housing (1), an inlet channel (22) for supplying, and an outlet channel (23) for discharging an electro-rheological fluid, and electro-rheological valves (1a, 1b, 2a, 2b) comprising an annular gap (8) which in each case connects an operating chamber (A and B) to the inlet channel (22) or the outlet channel (23) and whose boundary surfaces form electrodes for the generation of an electric field, the electro-rheological valves (1a, 1b, 2a, 2b) are formed by bores (6) which penetrate through the housing wall in the longitudinal direction and by mandrels (7) which are arranged in the bores (6) and are insulated from the housing (1), where the bores (6) and the mandrels (7) co-define annular gaps (8) of a constant gap width and the mandrels (7) can be connected to a high voltage and the housing (1) can be connected to earth potential.