The knowledge of the contact forces exchanged between pantograph and catenary (OverHead Line, OHL), together with the contact loss condition, is a very important mean to assess the overall performance of current collection. From the knowledge of the contact force it is possible to assess the dynamic performance of the pantograph-OHL system, moreover it can be possible perform diagnostic activities on the OHL. In addition, the contact force could be used as a feedback signal in order to set up an active control system for the pantograph. It is well known that the measurements of the contact force is a challenging task, therefore alternative approaches could be helpful in order to establish simples procedures for this task. In this paper the application of the EKF to the estimation of the contact force exchanged between pantograph and OHL is examined, first considering numerical test only, aimed to assess the level of uncertainties when considering as observed state displacement and velocity of the collectors and the articulated frame of the pantograph, and the displacements only. Finally, the procedure is applied to a real set of experimental signal, obtained during an experimental campaign carried out on an ETR500 high speed train, by UTMR.