Humanoids are being applied into society gradually in the aspect of human–robot interaction recently. The human spine plays an important role when performing natural human upper body postures. However, most of the humanoids only show tense body postures due to the limitations of their simple mechanical structures. We investigated that the human natural spine postures can be imitated by serially connected rigid links with a few joints by the analysis of human spine motion. In this report, we proposed a robotic spine composed of parallelogram actuation modules, and built a prototype. We also investigated the natural spinal postural appearances which are realized by the prototype.