Use of the water hydraulics is becoming more common, because of the increasing environmental awareness. Water hydraulics are behind in development from oil hydraulics. That is why the development of new components is essential. In this thesis we improved the concept of existing proportional directional control valve for water hydraulics. The valve is designed for operating pressures up to 35 MPa and flows of 60 l/min at the pressure difference of 2 MPa. We improved the design of the housing and control pistons. We also developed a new proportional magnet and manufactured the new valve. We did flow simulations, numerical calculations and measurements on the new valve. We have succeeded in improving the previous valve.