Abstract: This paper deal with a new foldable pipeline inspection robot that can be used for inspection of pipelines with 40 mm - 70 mm diameter. This reconfigurable robot has three powered wheel chains and each wheel chain is operated by a micro DC motor. Moreover the new wheel chain mechanism is foldable by using a new torsion spring and its backbone. Using this foldable mechanism, a small-sized robot whose external diameter is less than 40 mm can be designed. Validity of this new foldable wheel chain mechanism is proved through dynamic simulation using a commercial dynamic simulation program. Based on this, the stiffness of the torsion spring and the actuator size of DC motors are decided. As a result, a proto type of the pipeline inspection robot system is developed. It consists of a main body, two CMOS cameras, and two lighting devices. The validity of this robot system was proved by experimentation at the test bed, followed by a field test at an old apartment.