In this paper the mechanical design and kinematic analysis of a humanoid robot are presented. This robot is designed to perform as a soccer player, according to the current structure and dimensions restrictions stated by the International RoboCup Federation for the Kid-Size league in the RoboCup competition. The corresponding mechanism has 26 degrees-of-freedom (dof). It is composed by two legs (6 dof each), two arms (5 dof each), a torso (2 dof waist) and a head (2 dof). The direct and inverse kinematic analysis were carried out by means of applying the Denavit-Hartenberg methodology and using Screw Theory. The last one led to an analytical solution to the inverse kinematic problem, given that the mechanical design was correctly planned. As a future work, these mathematical models will be used in the elaboration of a simulator that permits to analyze the robot's movement and to generate adequate gait patterns.