The slip control is important for an adhesion force transmission between locomotive wheels and rails. The slip control consists of two tasks. The first task is the slip value detection and the second one is the evaluation of a slip value with a subsequent control action. These two tasks can be realized by many types of methods. Several detection methods use an adhesion coefficient or the adhesion force determination. Because of difficulty of the adhesion coefficient measurement during the train run the adhesion coefficient or the adhesion force has to be estimated. In this paper, the adhesion force is estimated by the Kalman filter. The Kalman filter uses the locomotive model and measured locomotive velocity. The Kalman filter is implemented in Matlab and also applied on measured data.