A new biped robot with a triangle configuration is presented and it is a planar closed chain mechanism.The scalability of three sides of the triangle is realized by three actuated prismatic joints.The three vertexes of the triangle are centers of three passive revolute joints coincidently.The biped mechanism for straight walking is proposed and its walking principle and mobility are explained.The static stability and the height and span of one step are analyzed.Kinematic analysis is performed to plan the gaits of walking on an even floor and going upstairs.A prototype is developed and experiments are carried out to validate the straight walking gait.Two additional revolute joints are added to form a modified biped robot which can follow the instruction of turning around.The turning ability is verified by experiments.As a new member of biped robots,its triangle configuration is used to impart geometry knowledge.Because of its high stiffness,some potential applications are on the way. A new biped robot with a triangle configuration is presented and it is a planar closed chain mechanism. The scalability of three sides of the triangle is realized by three actuated prismatic joints. The three vertexes of the triangle are centers of three passive revolute joints coincidently. The biped mechanism for straight walking is proposed and its walking principle and mobility are explained. The static stability and the height and span of one step are analyzed. Kinematic analysis is performed to plan the gaits of walking on an even floor and going up stairs. A prototype is developed and experiments are carried out to validate the straight walking gait.Two additional revolute joints are added to form a modified biped robot which can follow the instruction of turning around. Turning ability is verified by experiments. As a new member of biped robots, its triangle configuration is used to impart geometry knowledge. cause of its high stiffness, some potential applications are on the way.