This paper presents a lightly weighted hydraulic actuator that is designed mainly for robotic applications. This hydraulic cylinder will be used as the main actuator for the hydraulic humanoid robot HYDROïD. For implementation, the knee joint is taken as an example in order to execute the necessary steps to build the actuator from carbon fiber composite material. An optimization process is used to minimize the total weight of the actuator and satisfy its constraints. Meanwhile, the mechanical design with the integrated sensors is shown. In addition, results are discussed on the spot of the weight minimization and actuator performance. Finally, experimental testing is carried out to monitor the pressure and the position readings of the hydraulic cylinder.