In this article we investigate the dynamics of a five-link, passive bipedal robot. The passivity in this context stands for the ability of the robot to walk autonomously down an inclined surface without any external source of energy. Previous research efforts in passive walking were limited to four link models with knees or 2-link models without knees with a variety of mass distributions. In this paper we analyze the dynamics of a five-link robot with knees and upper body. We were successful in detecting three limit cycles that include three distinct upper body motions. We have investigated the structural stability of these cycles subject to variations in the upper body length. The results demonstrated that the stability can be improved with addition of linear dampers in the hip joints of the model. Also, our investigation demonstrated that erect body posture is only achievable when torsional springs are placed in the hip joints. (C) 2003 Published by Elsevier Ltd.