A robot component is provided as assembly units for assembling a robot toy with a great variety of configuration. The robot component has three connectors, i.e., a rotatable connector of a gear shaft, a laterally protruding connector of the gear shaft, and a receivable connector of a middle housing. These connectors are engaged with various joint members so several robot components are joined to each other to realize the complete robot toy. The robot toy has a master main-processor unit board provided in one of the robot components and joint control systems respectively provided in the other robot components. Each joint control system operates the robot component according to a predefined operation pattern when the master main-processor unit board transmits robot control signals.