A dynamically reconfigurable robotic system (DRRS) is one that can reconfigure itself to an optimal structure, depending on the purpose and environment. To realize this concept, the authors propose CEBOT (cell structured robot), which is a distributed robotic system consisting of separable autonomous units. These functional cells are able to communicate with each other and to approach, connect, and separate automatically. If single cells of CEBOT are damaged, they can be repaired or replaced automatically. Since CEBOT is capable of adapting itself to changing environments, it is a very flexible system applicable in space, factory, and hostile environments. The authors propose an optimal structure decision method that can determine cell type, arrangement, degree of freedom, and link length. It is applicable to fixed-base and mobile-base manipulators. A structure evaluation function, which is the sum of parameters relating to the number of work points, required positioning accuracy, torque, distance between given work points, and cell cost, is presented. Simulation results are given.<<ETX>>