Solid friction in mechanical control systems causes undesirable effects such as a jerking motion. To avoid such effects, identification of the velocity characteristics of solid friction is indispensable. It has already been reported that on-line estimation of the solid friction is possible by using standard Kalman filtering techniques. In this paper we discuss an application of a fixed-lag smoother to the solid friction estimation. Although this technique cannot be used on-line, the resulting estimate is more accurate than that which can be obtained by a standard Kalman filter. It is shown that there exists an appropriate number for the lag in the smoother to achieve efficient estimation. Simulation and experimental results are presented to show the effectiveness of the proposed technique.