In this paper, the importance of experimental evaluation of stiffness performance is pointed out for evaluating positioning errors and guaranteeing the effectiveness of a robotic walking system. Thus, a simple reliable procedure is proposed as based on a simplified version of Milli-CaTraSys (Milli Cassino Tracking System). Experimental tests are carried out on a biped locomotor that is named as WL-16RJI (Waseda Leg No. 16 Refined II) in dynamic conditions. The experimental tests provide useful information for both design and control purposes.