This paper presents the modeling and the design of the HYDROïD (HYdraulic anDROïD) humanoid robot. Our motivation related to the increase of understanding of human being locomotion and manipulation tasks achievement leads us to focus on the kinematical structure and the actuation aspects. The first part of this paper deals with a research work aimed to develop a new generation of three degrees of freedom (DOF) mechanism for humanoid robots. The main idea is to build hybrid 3DOF mechanism, which avoids the drawbacks of the serial and parallel mechanisms. The new solution has to merge the advantages of both classical (serial and parallel) structures in order to achieve optimal performances. The proposed mechanism can be used as a solution for several modules in humanoid robot such as ankle, hip, shoulder, wrist and neck. To illustrate our approach, the design of the ankle joint which is considered one of the more compact with high power capacity and low weight will be presented. The very important role played by this joint during walking, makes its design and control the first step of having a robust walking biped. The proposed solution fulfils the requirements induced by both geometrical and biomechanical constraints. In the second part, the paper will focus on the actuation of a humanoid robot, which is also still an open question and represents a big challenge. Demanding performances including high power to mass ratio, capability of producing high power at low speed within a small-occupied volume are some of the key issues that required careful consideration. These criteria aimed to increase autonomy of humanoid robots. A novel hydrostatic transmission actuator will be presented. The proposed actuator is controlled by displacement and has capacities for energy storage. This leads to an optimal solution in terms of power consumption. The input/output law of the proposed solution is detailed in order to show our ability to access to the payload “jerk”. The built prototype of HYDROïD robot and its properties are outlined. Finally, the preliminary results of the actuator performance and the 3DOF hybrid mechanism module are presented, demonstrating the novelty of the adopted solutions for HYDROïD robot.